(Highlighted individuals themselves received letters and are included in the list.)

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Rinat Akhmetshin

Who he is: A former Soviet military officer who now does lobbying work in the United States. During his service, his unit provided support for a military counterintelligence unit. Some officials believe he has ties to Russian intelligence, though he denies it.

Why he’s important: He joined his colleague Natalia Veselnitskaya, a lawyer linked to the Kremlin, at the June 9, 2016, meeting in Trump Tower predicated on providing information that would undermine Hillary Clinton’s campaign. The focus of the meeting instead reportedly focused on the Magnitsky Act — a law that resulted in sanctions on numerous prominent Russians. The law was a focus of the lobbying work undertaken by Veselnitskaya and Akhmetshin.

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Akhmetshin would be able to tell investigators about what happened in the meeting and how it came to be scheduled.

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American Media Inc.

What it is: The parent company of the tabloid newspaper National Enquirer.

Why it’s important: AMI has admitted to having worked with Michael Cohen , Trump’s former personal attorney, on a deal meant to cover up an alleged affair involving Trump. In August 2016, former Playboy model Karen McDougal sold the rights to any story involving her having a relationship with a married man to AMI. AMI never intended to run any such story.

AMI chief executive David Pecker later sought reimbursement from Cohen for the deal but was reportedly told by his attorneys that receiving such a payment would increase his exposure to criminal charges related to the payoff.

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Julian Assange

Who he is: The founder and head of WikiLeaks .

Why he’s important: An indictment obtained by special counsel Robert S. Mueller III indicates that in June 2016, WikiLeaks reached out to the hackers who accessed the Democratic National Committee’s network offering to host material. Assange would probably have information on those interactions and the eventual transfer of material stolen from Clinton campaign chairman John Podesta.

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He would also be able to provide information about possible contacts with the Trump campaign or with people tangentially connected to the campaign, such as Ted Malloch .

Christopher Bancroft Burnham

Who he is: Burnham is the chief executive of Cambridge Global Capital (not to be confused with Cambridge Analytica ). He also served on Trump’s transition team .

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Why he’s important: In addition to possible questions about his service on the transition team, Burnham was recently named to the board of En+ Group, the parent company of Russian aluminum giant Rusal. En+ was previously controlled by an oligarch named Oleg Deripaska, who employed Paul Manafort and Rick Gates before they were senior figures in Trump’s campaign.

The U.S. government recently lifted sanctions against En+ that were imposed after the Russian interference effort in the 2016 campaign.

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Stephen K. Bannon

Who he is: Trump’s former campaign CEO and adviser to his administration.

Why he’s important: Bannon could speak to a broad range of issues within the campaign and White House .

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Tom Barrack

Who he is: Barrack is a longtime business partner of Trump’s who also served as the head of Trump’s inaugural committee .

Why he’s important: There are a number of questions regarding fundraising and spending during the inaugural period about which Barrack could presumably offer information. His long history with Trump might also be of interest. He’s already been interviewed by Mueller’s team.

Tom Bossert

Who he is: Trump’s former homeland security adviser.

Why he’s important: Bossert received an email from K.T. McFarland after she’d spoken with Michael Flynn following one of Flynn’s conversation with former Russian ambassador Sergey Kislyak in December 2016. During these conversations, Flynn and Kislyak discussed Russia not retaliating against sanctions imposed by Barack Obama’s administration. The New York Times reported that Bossert then forwarded McFarland’s email to other transition officials, including Bannon , Reince Priebus and Sean Spicer . He disputes that report.

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After the inauguration, Bossert was present for a number of decisions in the White House , including some related to possible sanctions.

Matthew Calamari

Who he is: A longtime Trump Organization staffer who served as Trump’s bodyguard before being promoted to chief operating officer.

Why he’s important: During his testimony before the House Oversight Committee last week, Michael Cohen identified Calamari as being able to verify that Trump had inflated his assets for insurance purposes. Presumably Calamari could speak to other aspects of the Trump Organization as well.

Cambridge Analytica

What it is: A political data firm founded by Stephen K. Bannon and conservative donor Robert Mercer. It closed in 2018.

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Why it’s important: The firm became a subject of international attention when it was revealed that it had exploited Facebook’s terms of service to aggregate information on millions of people. The company used its data to develop profiles of voters that became central to its sales pitch.

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The Trump campaign hired Cambridge to help with its outreach efforts. Mueller’s team has reportedly been investigating if there was data passed from the Trump campaign to Russian actors, or vice versa. There have also been questions about possible outreach from Cambridge employees to WikiLeaks and Julian Assange .

Michael Caputo

Who he is: A former Trump campaign staffer who had previously worked with both Paul Manafort and Roger Stone . During the 1990s, he worked in Russia.

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Why he’s important: Caputo has also been interviewed by Mueller about his work for the Trump campaign .

Michael Cohen

Who he is: Trump’s former personal attorney.

Why he’s important: As revealed during his testimony last week, Cohen has a wealth of information about the Trump campaign and the Trump Organization . Of the most immediate interest to investigators will be Cohen’s involvement in a proposal to build a tower in Moscow, a project initiated by former Trump business partner Felix Sater .

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There’s also the question of Cohen’s role in the hush-money payments to Karen McDougal and adult-film actress Stormy Daniels, including the role of American Media Inc. and its CEO David Pecker . Cohen revealed last week that he had been paid by the Trump Revocable Trust .

Columbus Nova

What it is: A U.S. investment firm linked to a Russian company called Renova Group, which is owned by the oligarch Viktor Vekselberg .

Why it’s important: Columbus Nova paid Michael Cohen $500,000 for consulting help during the beginning of Trump’s presidency, and its chief executive, Andrew Intrater , gave $250,000 to Trump’s inaugural committee . There will be questions about what, if anything, those investments returned.

Concord Management and Consulting

What it is: A Russian consulting company under sanction by the U.S. government.

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Why it’s important: Concord and an affiliate company were identified in an indictment obtained by Mueller’s team as having helped bankroll the alleged Russian effort to interfere with the 2016 election over social media.

Mark Corallo

Who he is: A former spokesman for Trump’s legal team.

Why he’s important: Last year, it was reported that Corallo would tell Mueller about a conference call in which he participated. After Donald Trump Jr. 's initial explanation for the Trump Tower meeting — which he said was centered on adoption — Corallo reportedly was told by Trump’s communications staffer Hope Hicks that the truth, as contained in emails sent by Trump Jr., would “never get out.”

Jerome Corsi

Who he is: A conservative writer and conspiracy theorist associated with Roger Stone .

Why he’s important: Corsi and Stone exchanged a number of messages throughout 2016. Shortly after WikiLeaks began releasing material stolen from the DNC, Stone emailed Corsi (apparently at the behest of an official with the Trump campaign ) to see whether he could figure out what else WikiLeaks had. Corsi passed the request on to Ted Malloch , later telling Stone that two more drops were expected, one in August and one in October.

How Corsi might have known this and what he was told by Malloch are unclear.

Corsi also claims in a book that Stone asked him to tell WikiLeaks to drop material stolen from Podesta to distract from the release of the “Access Hollywood” tape Oct. 7, 2016 — a release that occurred on that day.

Randy Credico

Who he is: A New York-based radio host and associate of Roger Stone .

Why he’s important: Like Corsi, Credico had repeated interactions with Stone related to the WikiLeaks releases. After having interviewed Julian Assange , Credico exchanged texts with Stone about what might be expected. As the Oct. 7 release approached, Corsi appears to have indicated to Stone in text messages when there were expected delays.

Keith Davidson

Who he is: An attorney who represented both Stormy Daniels and Karen McDougal as they reached hush-money agreements with American Media Inc. and Michael Cohen .

Why he’s important: He can provide more details about the genesis of those agreements, including the extent to which the Trump campaign was involved and if Cohen identified that the goal was to influence the election. That point is central to the determination of criminal liability.

In a tweet, Davidson expressed his willingness to assist the probe.

Sheri Dillon

Who she is: A former attorney for Trump.

Why she’s important: Dillon and Stefan Passantino , at one point Trump’s deputy counsel in charge of ethics, have been accused by Democrats of making false statements to the Office of Government Ethics. After it was revealed that Trump had been repaying Michael Cohen for the hush-money payment to Daniels, questions arose about his having failed to report the debt on his financial disclosure documents.

Dillon’s role was raised during Cohen’s testimony last week.

Annie Donaldson

Who she is: Former chief of staff to former White House counsel Donald McGahn .

Why she’s important: Donaldson joined the White House in early March 2017 and would probably have been involved in or known about key moments affecting the counsel’s office, such as the timeline of the firing of Michael Flynn or the push to fire former FBI director James B. Comey. She was also asked for any documents related to Trump’s subsequent efforts to fire Mueller — efforts that reportedly had McGahn considering his resignation.

Paul Erickson

Who he is: A conservative political operative.

Why he’s important: Erickson had a close relationship with Maria Butina, a Russian who in December pleaded guilty to conspiracy to act as an agent of the Russian government. Butina and another Russian, Alexander Torshin, allegedly sought to build relationships with Republican officials by leveraging the National Rifle Association . Torshin at one point sought a meeting with Donald Trump Jr. The two met briefly at an NRA event in May 2016.

Tony Fabrizio

Who he is: A pollster who had worked for Paul Manafort and who did work for the Trump campaign .

Why he’s important: Fabrizio’s polling appears to have ended up in the hands of Konstantin Kilimnik, a Russian believed to be linked to Russian intelligence who had worked with Manafort in the past. At an Aug. 2, 2016, meeting where he was accompanied by Rick Gates , Manafort is believed to have given polling apparently conducted by Fabrizio to Kilimnik, who then reportedly passed it to two Russian oligarchs.

Fabrizio could offer more information about what the polling showed.

Federal Bureau of Investigation

Why it’s important: The FBI was asked for information on a wide range of information including Michael Flynn , the Comey firing and possible information about contacts between the Trump campaign and Russian individuals.

Michael Flynn

Who he is: An early Trump supporter, Flynn briefly served as Trump’s national security adviser.

Why he’s important: Flynn could speak to a range of issues. Those include a December 2016 meeting at Trump Tower with former Russian ambassador Sergey Kislyak in which Flynn and Jared Kushner allegedly sought to establish a communications back channel with Russia. Flynn could also speak to his conversations with Kislyak later that month related to upcoming sanctions on Russia — the issue for which he eventually lost his position with the White House after it became publicly obvious that his story about the conversation differed from Vice President Pence’s. That it took so long to fire Flynn appears to be something of interest to investigators.

Flynn also met with Russian President Vladimir Putin in December 2015 at an event in Moscow. After leaving the White House, he attracted negative attention for his work lobbying for Turkey through his company Flynn Intel Group . Part of that work also apparently involved advocating a deal aimed at bringing nuclear power plants to Saudi Arabia. A whistleblower alleged that Flynn texted about the proposed deal moving forward during Trump’s inauguration.

Flynn, Michael Flynn Jr. and Flynn Intel Group were also identified by Peter Smith as an ally in Smith’s effort to dig up any emails that might have been hacked from Clinton’s private email server.

Flynn Intel Group

What it is: Michael Flynn ’s consulting firm.

Why it’s important: See above.

Michael Flynn Jr.

Who he is: Michael Flynn ’s son.

Why he’s important: Flynn Jr. has been an outspoken defender of his father. The document request sent to Flynn Jr. covers a broad range of possible communications — including any discussion of possible pardons from Trump. Flynn Jr. was also identified by Peter Smith as connected to his effort.

Frontier Services Group

What it is: A company created and led by Blackwater founder Erik Prince .

Why it’s important: It’s not immediately clear. In May, The Post reported on questions about Frontier’s work, though it doesn’t seem to be related to Trump.

Alan Garten

Who he is: Chief legal officer to the Trump Organization .

Why he’s important: The focus of the document requests for Garten is on payments from foreign companies to Trump Organization businesses. (Under the Constitution, there are limits on money that the president can receive from foreign entities.) Garten can also inform investigators about the proposed development of a tower in Moscow that was under discussion during the campaign.

Rick Gates

Who he is: Trump’s former deputy campaign chairman and a member of the Trump inaugural committee . Before that, Gates worked closely with Paul Manafort .

Why he’s important: Gates, who’s cooperating with the Mueller probe, can answer a range of questions about subjects of interest to investigators, including possible Russian contacts. He’s also reported to have asked inaugural donors to pay vendors directly, sidestepping reporting requirements.

General Services Administration

What it is: An agency that serves as an office manager for the federal government.

Why it’s important: The GSA holds the lease for the building on Pennsylvania Avenue that’s now operated as a hotel by the Trump Organization . As such, it can provide information about the development of that lease, information offered by the Trump Organization as the lease was under discussion and, possibly, data on foreign use of the Trump hotel property.

Rob Goldstone

Who he is: A music promoter who represents a Russian singer named Emin Agalarov.

Why he’s important: Goldstone was the person who first proposed a meeting between Donald Trump Jr. and a Kremlin-linked attorney who allegedly had information that could implicate Clinton. He pitched the meeting and helped facilitate the date and time on which it would occur in early June 2016. He ended up attending, along with Trump Jr., Paul Manafort , Jared Kushner and Rinat Akhmetshin.

J.D. Gordon

Who he is: A Trump campaign staffer.

Why he’s important: Gordon helped lead Trump’s foreign policy advisory team, two members of which — George Papadopoulos and Carter Page — had demonstrated connections to Russian actors during the campaign.

Gordon was involved in discussions before the Republican convention in 2016 in which the party’s position on Ukraine was changed in a way viewed as favorable to Russia. He was also close with Maria Butina, who he invited to his birthday party shortly before the election.

Rhona Graff

Who she is: Trump’s longtime assistant and scheduler.

Why she’s important: Graff could provide information on a number of meetings and discussions in which Trump was involved over the 2016 election. (Trump generally worked from his Trump Organization office while running for president.)

She was also identified by Michael Cohen as being likely to have important information on his conversations with Trump.

Hope Hicks

Who she is: A former Trump campaign and White House communications official.

Why she’s important: Hicks was close to many decisions made by Trump over 2016 and 2017. That includes the conversation in which Mark Corallo suggests she said that emails from Donald Trump Jr. contradicting his statement about the Trump Tower meeting would never be public.

Hicks was also asked for any documents related to Michael Flynn ’s firing.

Dylan Howard

Who he is: The former editor in chief for the National Enquirer.

Why he’s important: Howard was identified in documents related to Michael Cohen ’s plea agreement as having participated in conversations related to the hush-money agreements Cohen later brokered. Those documents also indicate that both Howard and his boss, David Pecker , personally informed Cohen about the stories being pitched by McDougal and Daniels.

Howard can speak not only to the genesis of those agreements but also to the extent to which they focused on the 2016 presidential campaign.

Presidential Inaugural Committee

What it is: The nonprofit entity that raised money for and organized Trump’s inauguration.

Why it’s important: The committee has come under fire for its fundraising and spending. Committee documents could shed light on how money was raised, what was promised and details on where money was spent.

Andrew Intrater

Who he is: The founder of Columbus Nova .

Why he’s important: Intrater, as founder of a company linked to oligarch Viktor Vekselberg , met with Michael Cohen shortly before the 2016 election. The company later signed a contract with Cohen that paid him $500,000. Intrater himself gave $250,000 to the inaugural committee.

Intrater is also Vekselberg’s cousin.

Department of Justice

Why it’s important: As with the FBI , investigators seek a wide range of documents on a number of issues.

Brittany Kaiser

Who she is: A former executive at Cambridge Analytica .

Why she’s important: Kaiser was director of business development for the company and has been asked for information related to possible contacts with Russia or with WikiLeaks .

Irakly Kaveladze

Who he is: The U.S. representative of the Crocus Group, the company owned by Aras Agalarov.

Why he’s important: Kaveladze also attended the June 2016 Trump Tower meeting organized by Rob Goldstone on behalf of Agalarov’s son, Emin Agalarov. Kaveladze, like Rinat Akhmetshin and Goldstone, could discuss the content of the meeting but, as a representative of Crocus Group, might also have more information about how Agalarov came to want to organize the meeting in the first place.

Jared Kushner

Who he is: Trump’s son-in-law.

Why he’s important: As with Stephen K. Bannon , the documents requested from Kushner cover a broad range of activity — as does the information he might be able to provide investigators.

Kushner Companies

What it is: The private company founded by Jared Kushner ’s father, Charles, which Jared took over in 2005.

Why it’s important: There have been several deals involving Kushner Cos. properties that have raised eyebrows, including a Deutsche Bank loan that came just before Election Day and links between a company that bailed out a struggling Kushner property last year and the government of Qatar.

Corey Lewandowski

Who he is: Trump’s original campaign manager.

Why he’s important: Present for the first year of Trump’s campaign, Lewandowski would have been privy to many of the early decision-making processes that occurred. Investigators are seeking a similarly sweeping set of documents from Lewandowski as they are Stephen K. Bannon .

Ronald Lieberman

Who he is: Vice president of management and development at the Trump Organization .

Why he’s important: Lieberman was identified by Michael Cohen during his testimony last week as being aware that Trump inflated his assets when providing information to an insurance company.

Ted Malloch

Who he is: A conservative writer based in Britain.

Why he’s important: Malloch has claimed that he was an informal adviser to the Trump campaign in 2016. More importantly, he’s believed to have some connection to WikiLeaks . When Roger Stone asked Jerome Corsi to find out more information about WikiLeaks’s upcoming document releases in July 2016, Corsi passed the request on to Malloch. Corsi later gave Stone information about further releases.

Jason Maloni

Who he is: Paul Manafort ’s spokesman.

Why he’s important: Maloni, who testified before Mueller’s grand jury, was asked for a number of documents, including any documents related to a possible pardon for Manafort. The question of whether Manafort was expecting a pardon has become salient after the revelation that Manafort lied to Mueller’s investigators.

Paul Manafort

Who he is: Former campaign chairman for the 2016 Trump campaign .

Why he’s important: Manafort not only led the campaign but his vast history of work for Russia-connected individuals and the various questionable actions he undertook while working for the campaign — including extending an offer for a private campaign briefing to oligarch Oleg Deripaska — also make him an important potential witness.

Among other things, Manafort, if he chose to cooperate, could offer more information about the Trump Tower meeting, about the sharing of polling with Konstantin Kilimnik and about Trump’s approach to or awareness of Russian interference efforts.

K.T. McFarland

Who she is: Former deputy national security adviser under Michael Flynn .

Why she’s important: Flynn and McFarland worked together closely after he was named national security adviser-designate by Trump in November 2016.

The next month, Flynn called McFarland after speaking with former ambassador Kislyak. McFarland, in turn, sent an email about the call to other transition officials.

“If there is a tit-for-tat escalation Trump will have difficulty improving relations with Russia,” the email read, “which has just thrown U.S.A. election to him.” It’s not clear what she meant by that last phrase.

Donald McGahn

Who he is: Former White House counsel.

Why he’s important: McGahn was involved in a number of key decisions in the first two years of the Trump White House, including the firings of Michael Flynn and James B. Comey and Trump’s reported efforts to oust Mueller.

George Nader

Who he is: A businessman with ties to the United Arab Emirates.

Why he’s important: Nader participated in a meeting in the Seychelles during the Trump transition period in which Erik Prince had a conversation with a Russian businessman, Kirill Dmitriev, who’s believed to be close to Putin. That meeting is alleged to have been a possible effort to establish a private back channel between Trump’s team and Russia and was reportedly set up by the United Arab Emirates, for which Nader worked as an adviser.

National Rifle Association

Why it’s important: There have been questions about the NRA’s advocacy for Trump during 2016 for some time, centered on whether the organization accepted money from Russian interests that helped pay for its advertising.

The NRA denies the allegation. It’s not clear what documents were requested.

Alexander Nix

Who he is: Former CEO of Cambridge Analytica .

Why he’s important: In addition to the extant questions about Cambridge Analytica’s role in the 2016 election, Nix admits to having reached out to WikiLeaks during the 2016 campaign to offer to help Julian Assange ’s group release deleted emails from Hillary Clinton’s private email server — documents that there’s no evidence Assange or WikiLeaks had.

Sam Nunberg

Who he is: Nunberg began working as a political adviser to Trump in 2014 before being fired in July 2015.

Why he’s important: Nunberg had connections with a number of people central to the Trump campaign , most importantly Roger Stone . Mueller’s team requested and received emails from Nunberg to a number of campaign officials on this list.

Carter Page

Who he is: A former Trump campaign foreign policy adviser.

Why he’s important: Page was first interviewed by the FBI in 2013 after a suspected Russian agent identified him as a target for recruitment. In July 2016, while working for the campaign, he traveled to Moscow, where he met with a deputy prime minister who, he said in an email back to the campaign, had expressed support for Trump’s candidacy.

The dossier of reports alleging collusion between the campaign and Russia written by former British intelligence official Christopher Steele alleged deeper ties between Page and Russian actors. In October 2016, after leaving the campaign, Page was the target of a surveillance warrant by the FBI.

Page, like J.D. Gordon , was asked to provide documents related to the change in the Republican platform.

George Papadopoulos

Who he is: A former Trump campaign foreign policy adviser.

Why he’s important: Papadopoulos triggered the FBI’s counterintelligence investigation when he told an Australian diplomat in May 2016 that he’d been informed that Russia had thousands of emails compromising Clinton. That information had been given to him by a Russia-linked professor based in Britain.

Brad Parscale

Who he is: Trump’s 2016 campaign data chief and 2020 campaign manager.

Why he’s important: Parscale, as one of the senior officials in the Trump campaign , was asked for a range of documents. Most central to the investigation, though, is the request for documents about “[d]iscussions or attempts to provide or receive election information, campaign data, or campaign communications with, to, or from foreign entities or individuals in connection with the 2016 U.S. Presidential primary or general elections.”

It’s been reported that Mueller is looking at whether the campaign and Russian actors shared data. The question above gets to that directly. (Interestingly, Parscale wasn’t asked for any documents about Cambridge Analytica specifically, though the section above may get at related questions.)

Stefan Passantino

Who he is: Former deputy White House counsel in charge of ethics.

Why he’s important: Passantino and Sheri Dillon have been accused by Democrats of making false statements to the Office of Government Ethics. After it was revealed that Trump had been repaying Michael Cohen for the hush-money payment to Daniels, questions arose about his having failed to report the debt on his financial disclosure documents.

David Pecker

Who he is: CEO of American Media Inc.

Why he’s important: Pecker was involved in discussions centered on the hush-money payment made to Karen McDougal in August 2016, a payment allegedly made in coordination with Michael Cohen and Trump. Pecker expected to be repaid by Trump but later rescinded that request, apparently after his attorneys suggested that it might further implicate him in campaign finance crimes.

A document filed as part of Cohen’s plea agreement indicates that both Pecker and the National Enquirer’s editor in chief, Dylan Howard, personally informed Cohen about the stories being pitched by McDougal and Daniels. That probably stemmed from a meeting in August 2015 where Pecker told Cohen and another person — probably Trump — that AMI would help kill stories detrimental to Trump’s candidacy.

Reince Priebus

Who he is: Trump’s former White House chief of staff.

Why he’s important: Priebus led Trump’s staff during the period in which both Michael Flynn and James B. Comey were fired. He was also part of the transition team and received the email about Flynn’s conversations with the Russian ambassador.

Erik Prince

Who he is: The founder of Frontier Services Group and brother of Education Secretary Betsy DeVos.

Why he’s important: Prince met with Kirill Dmitriev, a Russian businessman believed to be close to Putin, in the Seychelles in early 2017. The meeting was alleged to have been a possible effort to establish a back channel with the Russian government, an allegation Prince denies. Prince says he was invited to the meeting by Mohammed bin Zayed al-Nahyan .

Mohammed bin Zayed al-Nahyan

Who he is: The crown prince of Abu Dhabi, United Arab Emirates.

Why he’s important: Mohammed bin Zayed al-Nahyan encouraged Erik Prince to meet with a connected Russian businessman shortly before the inauguration in 2017 but, a few weeks earlier, had a secret meeting at Trump Tower with Jared Kushner , Michael Flynn and Stephen K. Bannon . The Seychelles meeting involving Prince was allegedly intended to set up a back channel with Russia — also the alleged goal of a Trump Tower meeting in early December 2016 involving Kushner, Flynn and the Russian ambassador.

Donald J. Trump Revocable Trust

What it is: The business entity created to distance Trump from the day-to-day workings of the Trump Organization .

Why it’s important: The trust was the source of payments reimbursing Michael Cohen for the hush money he paid Stormy Daniels shortly before the election. Documents related to those payments were requested from the trust, as were any documents that might suggest foreign payments to the Trump Organization.

Anatoli Samochornov

Who he is: A translator who once contracted with the State Department.

Why he’s important: Samochornov joined the Trump Tower meeting in June 2016, which was also attended by Donald Trump Jr. , Paul Manafort , Jared Kushner and Rinat Akhmetshin . He could potentially offer more information about that conversation.

Felix Sater

Who he is: A longtime business partner of Trump’s who pitched Michael Cohen on the proposal for a development in Moscow.

Why he’s important: Sater, who in the past has worked as an informant for the federal government, was integral to the Moscow proposal. He could provide investigators with information about the duration of conversations about the project as well as what he had learned from both Cohen and Russian officials about how the proposal was progressing.

For example, Cohen had a conversation with an assistant to Putin’s spokesman on Jan. 20, 2016. The next day, Sater informed Cohen that he’d gotten a call from Putin’s office. The content of that call isn’t known.

Sater also worked on the project with a former general in the Russian intelligence agency.

SCL Group Limited

What it is: The parent company of Cambridge Analytica .

Why it’s important: As with the various former Cambridge staffers on this list — Alexander Nix, Julian David Wheatland and Brittany Kaiser — investigators are seeking information about possible data links to Russia.

One noteworthy detail is the request from those individuals (and many others) for “[a]ny contacts, direct or indirect, from January 1, 2016 to the present between Paul Manafort and/or Rick Gates and any of the following individuals: Konstantin Kilimnik, Serhiy Lyovochkin, and/or Rinat Akhmetov.” That’s a reference to the polling information shared by Manafort with Kilimnik, which he passed on to the oligarchs Lyovochkin and Akhmetov (not to be confused with Rinat Akhmetshin ).

Jay Sekulow

Who he is: Attorney for President Trump.

Why he’s important: Sekulow, like Donald McGahn , was asked for a broad range of information related to the Trump administration. He would have access to a great deal of information about Trump and the presidency, but it’s unlikely he would or could provide it.

Jeff Sessions

Who he is: Trump’s former attorney general.

Why he’s important: Sessions could provide investigators with information about the firing of James B. Comey as well as Comey’s descriptions of his interactions with Trump, which he indicates he often shared with Sessions. He could also corroborate reports that Trump sought to fire Mueller or Deputy Attorney General Rod J. Rosenstein.

Among the other documents requested from Sessions were any that related to possible pardons for Paul Manafort , Michael Flynn or Michael Cohen .

Estate of Peter Smith

What it is: The documents and material left behind by Peter Smith, a Republican activist.

Why it’s important: The Wall Street Journal reported that Smith had undertaken an effort to dig up emails from Clinton’s private email server that may have been stolen by hackers. (There’s no evidence that they were.) In late 2015, he met with Michael Flynn , before Flynn began working for the Trump campaign, and claimed broader connections to the Trump campaign. He worked with a small team, including John Szobocsan .

Smith is believed to have killed himself shortly after the Journal’s first report about his efforts was made public, “weeks after telling friends that he believed he had finally obtained the missing emails, according to a person familiar with the matter.” Part of Smith’s effort involved asking experts such as Matt Tait to verify material he had acquired.

Sean Spicer

Who he is: Trump’s former press secretary.

Why he’s important: Spicer’s tenure at the White House overlapped with the firings of Michael Flynn and James B. Comey. In particular, though, Spicer’s representations of the Flynn firing during a Feb. 14, 2017, news briefing seem to have captured investigators’ interest.

Roger Stone

Who he is: A longtime aide to Trump.

Why he’s important: Stone repeatedly alleged connections to WikiLeaks during the campaign. Last week, Michael Cohen testified that he was present for one of the first times Stone did so: an alleged call to Trump in July 2016 predicting the imminent release of emails by WikiLeaks.

It’s not clear how he might have known this, but a campaign official soon asked Stone to see what else WikiLeaks had. Stone emailed Jerome Corsi , who passed on the request to Ted Malloch . After Randy Credico interviewed Julian Assange in August 2016, Stone began texting with him and making public predictions about WikiLeaks’s plans based on that information.

Stone did have direct contact with WikiLeaks — centered on WikiLeaks’s insistence that he stop claiming that he had spoken with them.

John Szobocsan

Who he is: A partner of Peter Smith ’s.

Why he’s important: Szobocsan worked with Smith on his effort to uncover emails stolen from Clinton’s private email server. He has been interviewed by Mueller’s team multiple times.

Matt Tait

Who he is: A former British spy who was among the first to connect Russia to material stolen from the DNC.

Why he’s important: Tait was contacted by Peter Smith and asked to help verify material that Smith had obtained that he believed might have been emails hacked from Clinton’s private email server. When Tait suggested that the hackers who had provided Smith with the material might be Russian — if it was authentic at all — he indicates that Smith didn’t seem to care.

Tait spoke with both Smith and John Szobocsan by phone but never saw the allegedly hacked material.

Eric Trump

Who he is: Trump’s son and a senior campaign adviser.

Why he’s important: Eric Trump wasn’t as centrally involved in many of the questionable issues as Donald Trump Jr. , but investigators are still seeking a broad range of possible documents related to his awareness of issues included in this article.

The Trump campaign

Why it’s important: The campaign has been asked for a range of documents related to individuals on the list. Among them are any documents related to Michael Cohen ’s payment to Stormy Daniels — a payment that he and federal prosecutors allege was related to the campaign.

Donald Trump Jr.

Who he is: Trump’s son and a senior campaign adviser.

Why he’s important: Last March, we outlined the various reasons it was strange that Trump Jr. hadn’t yet talked to Mueller. The list is now longer: His involvement in the genesis of the Trump Tower meeting, his efforts to cover that meeting up, questions about his having told Trump about the meeting, his knowledge of the Trump Organization ’s business in Russia and his involvement in the Moscow project with Michael Cohen .

The documents requested by investigators cover nearly every subject on this list, presumably under the assumption that Trump Jr. and Trump would have had conversations about many of them.

Trump Foundation

What it is: Trump’s defunct private charity.

Why it’s important: The charity for years was involved in questionable activity, as The Post’s David Fahrenthold has documented.

Specifically, though, Trump is alleged to have used the charity to bolster his 2016 campaign. At one point, Allen Weisselberg allegedly contacted Corey Lewandowski — Trump’s campaign manager — to ask how charitable donations could be distributed to benefit the campaign.

Trump Organization

What it is: Trump’s private business.

Why it’s important: For a variety of reasons. Questions about Trump’s past business relationships have swirled since he began running for office, questions that remain in part because of the president’s refusal to release his tax returns. Among the documents sought by investigators are ones related to Michael Cohen ’s payment to Stormy Daniels and the way in which he was repaid.

Trump transition team

What it is: The group of advisers who worked on ensuring that Trump was prepared to assume control of the government.

Why it’s important: Among other documents, investigators are seeking information about Michael Cohen ’s contract work during the period between the election and the inauguration. There have been questions raised about how Cohen might have tried to deliver for his consulting clients, which such documents might help answer.

Viktor Vekselberg

Who he is: A Russian oligarch who runs the Renova Group.

Why he’s important: A firm linked to Renova, Columbus Nova , hired Michael Cohen to act as a consultant for the first half of 2017. Vekselberg also attended Trump’s inauguration — and was at the December 2015 dinner where Michael Flynn met Putin.

Allen Weisselberg

Who he is: Chief financial officer of the Trump Organization .

Why he’s important: Weisselberg first popped up in the Russia investigation when it was revealed that he was providing information to federal investigators about the hush-money payments to Stormy Daniels and Karen McDougal. During his testimony last week, Michael Cohen identified Weisselberg as a source of information about the specifics of those agreements.

In fact, Cohen recommended investigators talk to Weisselberg about a wide range of subjects. As CFO of the private Trump Organization, he could offer insight into a number of different areas. Included in the document requests was any information about foreign payments coming into the Trump Organization since Trump’s inauguration, documents related to the proposed Moscow deal and information about any Russian money coming into the Trump Organization.

Weisselberg was also involved in the Trump Foundation, at one point allegedly contacting Corey Lewandowski — Trump’s campaign manager — to ask how charitable donations could be distributed to benefit the campaign.

Julian David Wheatland

Who he is: Cambridge Analytica ’s CEO until its dissolution and the chairman of SCL Group, the predecessor to Cambridge.

Why he’s important: As with Alexander Nix and Brittany Kaiser , Wheatland was asked for information about possible contacts with Russia or WikiLeaks .

White House

Why it’s important: Documents sought by investigators cover a broad range of the issues on this list.

WikiLeaks

What it is: An organization that publishes material often obtained from government agencies.

Why it’s important: WikiLeaks obtained material stolen from the Democratic National Committee in July 2016 and, at some point that same year, data stolen from Clinton campaign chairman John Podesta. The material is believed to have been stolen by hackers linked to Russian intelligence.

During the campaign, Roger Stone repeatedly claimed to have contact with WikiLeaks and its founder Julian Assange , which WikiLeaks denied. (Stone did seem to have information about upcoming releases that suggested some connection.) Late in the campaign, WikiLeaks also reached out to Donald Trump Jr. over Twitter, though nothing significant appears to have been shared.