The firing of Jeff Sessions and his replacement on an interim basis by a man who has expressed open hostility to the Mueller investigation and in whose loyalty President Trump has expressed confidence marks a major moment in the course of the Russia investigation.

It is a profoundly dangerous moment: The president fired the attorney general, as he once fired the FBI director, for plainly illegitimate reasons: because the attorney general acted appropriately on an investigative matter in which Trump himself has the deepest of personal interests. Trump does not even pretend there are other reasons. He removed the attorney general because the attorney general did not protect him from investigation. Yes, the president has the raw power to do this. But as was the case with the firing of James Comey, it is an abuse of the power he wields.

Jeff Sessions will not go down in history as a great attorney general—or even a good attorney general. He was not admired within the Justice Department. He showed little leadership. He spoke up only weakly on behalf of the department he led.

Yet Sessions performed two great public services as attorney general for which the public owes him a debt of gratitude: He recused himself from the Russia investigation on the advice of the Justice Department’s career ethics officials, and he then subjected himself to more than a year of abuse—some public, some private—from the president of the United States designed to force him from office in humiliation. By remaining in place, Sessions allowed his deputy, Rod Rosenstein, to supervise and protect the Russia investigation. The combination of Sessions’s recusal and Rosenstein’s conduct has permitted Robert Mueller’s investigation to proceed in the face of President Trump’s relentless misconduct and efforts to discredit it.

This public service lasted barely 18 hours after the midterm elections, in which the Democrats secured control of the House of Representatives and Republicans added to their Senate majority.

Jeff Sessions has now left his post as attorney general and has been replaced on an acting basis by a man about whom a significant measure of anxiety is only prudent.

The situation is changing quickly, but here’s what we know so far. Just before 3 p.m. on Wednesday, Sessions submitted a letter of resignation “at [Trump’s] request.” Initial news reports indicate that Trump did not speak directly to Sessions but that White House Chief of Staff John Kelly reached out to the attorney general to request his departure. Trump quickly announced on Twitter that Sessions’s chief of staff, Matthew Whitaker, would take over as acting attorney general:

....We thank Attorney General Jeff Sessions for his service, and wish him well! A permanent replacement will be nominated at a later date. — Donald J. Trump (@realDonaldTrump) November 7, 2018

Sessions’s departure is effective immediately; he reportedly asked to stay in his role until the end of the week but was informed by Kelly that he would need to depart on Wednesday evening. According to a Justice Department spokeswoman, Whitaker will immediately assume control of the Mueller probe from Deputy Attorney General Rosenstein.

Sessions’s removal from the Justice Department and Rosenstein’s handoff of oversight of the Mueller probe to Whitaker raises a number of discrete though related questions.

The immediate question is whether Whitaker will seek to impede the Mueller investigation. His public statements on the subject, to put the matter mildly, do not inspire confidence. Here’s a sampling:

As the Washington Post noted on Oct. 10—when it reported that Trump had spoken with Whitaker about assuming Sessions’s role—Whitaker argued in a CNN.com op-ed that any investigation by Mueller into the finances of Trump and his associates could be a “red line.”

A month before his CNN op-ed was published, Whitaker said on the network that “I could see a scenario where Jeff Sessions is replaced by a recess appointment and that attorney general doesn't fire Bob Mueller but he just reduces his budget to so low that his investigations [sic] grinds to almost a halt.”

He defended Donald Trump Jr.’s 2016 meeting with a Russian lawyer in Trump Tower, saying that he would have taken the meeting as well.

Immediately after Trump fired James Comey as FBI director, Whitaker penned an opinion article in the Hill defending the dismissal and making the case against the appointment of a special counsel.

While Whitaker’s Twitter account is mostly about football, he tweeted a link to an article referring to the Russia investigation as a “lynch mob” in August 2017:

Worth a read. "Note to Trump's lawyer: Do not cooperate with Mueller lynch mob" https://t.co/a1YY9H94Ma via @phillydotcom — Matt Whitaker (@MattWhitaker46) August 7, 2017

He also criticized the special prosecutor’s search of the home of former Trump campaign chairman Paul Manafort as “designed to intimidate”:

Do we want our Gov't to "intimidate" us? Hmm -FBI's Manafort raid incl. a dozen agents, 'designed to intimidate,' | https://t.co/KAHQq26q2M — Matt Whitaker (@MattWhitaker46) August 25, 2017

Whitaker made these comments before Sessions hired him as his chief of staff in September 2017. Nevertheless, this is a man who has repeatedly expressed publicly his skepticism of the Russia investigation and his view that it should be reined in, and has also commented on the substantive conduct of people within the investigation’s gaze.

All of this creates some uncertainty as to how long Whitaker will oversee the probe—or, at least, how long he should. Like Sessions, Whitaker may be obligated to recuse himself from the Mueller investigation. The relevant Justice Department guideline is Section 45.2 of Title 28 of the Code of Federal Regulations, which states that “no employee shall participate in a criminal investigation or prosecution if he has a personal or political relationship with” either “any person or organization substantially involved in the conduct that is the subject of the investigation or prosecution” or “any person or organization which he knows has a specific and substantial interest that would be directly affected by the outcome of the investigation or prosecution.”

Although the regulations do not indicate that Whitaker’s public statements alone necessarily require recusal, Whitaker has other connections to people whose conduct is at issue in the matter. For instance, the regulations define a political relationship as “a close identification with an elected official, a candidate (whether or not successful) for elective, public office, a political party, or a campaign organization, arising from service as a principal adviser thereto or a principal official thereof.” Rebecca Ballhaus of the Wall Street Journal reports that Whitaker chaired the 2014 Iowa state treasurer campaign of Sam Clovis, who went on to serve in the Trump campaign and administration and who, Ballhaus notes, is now a grand jury witness in the Mueller investigation. The Des Moines Register reported Whitaker’s chairmanship of Clovis’s campaign during the campaign itself. What’s more, in a text message to Ballhaus after Whitaker’s appointment, Clovis wrote that he was “proud of my friend,” referring to Whitaker, raising the question of whether there is a personal relationship as well.

There is an important process point here: Under the same Justice Department regulation mentioned above, Whitaker is obligated to seek guidance from career ethics attorneys regarding whether he should recuse. This is the process Jeff Sessions used in determining that the rules required that he recuse, and Deputy Attorney General Rod Rosenstein also sought guidance regarding his obligations, though Justice officials determined that his recusal was not required. If Whitaker either does not obtain an ethics opinion from career officials or if he departs from that guidance, that would be a serious red flag. Notably, the Washington Post reports that Trump “has told advisers that Whitaker is loyal and would not have recused himself from the investigation.” This raises a question about whether the president knows something about Whitaker’s intentions regarding recusal.

Whitaker’s service as acting attorney general is governed by the Federal Vacancies Reform Act (FVRA), which states that when a vacancy occurs in a Senate-confirmed position because an officer “dies, resigns, or is otherwise unable to perform the functions and duties of the office” the president can designate, among other possible persons, “an officer or employee of such Executive agency to perform the functions and duties of the vacant office temporarily in an acting capacity” for up to 210 days. The employee or officer must have served in the agency for 90 days in the previous 365-day period, and the employee or officer must have a General Schedule (GS) level of at least GS-15. During the cycles of threats from the White House to fire Sessions and Rosenstein, legal analysts suggested that the FVRA may not allow a president to appoint an acting official to replace someone he has fired. Functionally, Sessions’s resignation at the president’s request is a firing. But as a formal matter, Sessions resigned, meaning that the president may install Whitaker as his replacement without violating the statute. Still, even if the FVRA is not at issue, there may be other legal concerns with the appointment, as Steve Vladeck noted on this evening’s Lawfare Podcast.

But if Whitaker does not recuse and actually supervises the investigation, he will be able to interfere with it if he chooses to do so. In the wake of rumors in September of Rosenstein’s removal, two of us (Hennessey and Wittes) posed the question: “What happens if the president is ultimately able to install a loyalist to oversee the special counsel investigation?” Such a loyalist, the post argued, has several avenues for causing mischief within the Mueller investigation. These include firing Mueller, although this could have other political repercussions, particularly come January.

Short of dismissing the special counsel, an acting attorney general who wanted to disrupt the investigation would have a number of wrenches to throw in its machine. He could, for example, aid the efforts of congressional Republicans hostile to the Mueller probe, such as Bob Goodlatte and Devin Nunes, who have actively sought information about the FBI’s counterintelligence investigation. He could also stymie the investigation by means of intrusive oversight. When Rosenstein appointed Mueller, he explicitly applied the special counsel rules set forth at 28 CFR 600.4-600.10. These rules define the special counsel’s powers and, importantly, the scope of the relationship between the special counsel and the attorney general. The new acting attorney general will not easily be able to alter the existing scope of the investigation. However, the regulations also require the special counsel to “consult with appropriate offices within the Department for guidance with respect to established practices, policies and procedures of the Department, including ethics and security regulations and procedures.” And the special counsel is required to notify the attorney general “of events in the course of the investigation in conformity with the Departmental Guidelines with respect to Urgent reports.” Practically, Mueller must provide advance notice to the attorney general of any “major developments,” such as filing criminal charges. As the September Lawfare article noted:

Such information-sharing alone could be a problem if sensitive law enforcement information improperly made its way to the White House—much less to subjects of the investigation. Beyond such obviously improper conduct, however, an acting attorney general could determine under the rules that a proposed action should not be pursued at all. The applicable regulation reads: “The Special Counsel shall not be subject to the day-to-day supervision of any official of the Department. However, the Attorney General may request that the Special Counsel provide an explanation for any investigative or prosecutorial step, and may after review conclude that the action is so inappropriate or unwarranted under established Departmental practices that it should not be pursued. In conducting that review, the Attorney General will give great weight to the views of the Special Counsel.” Note that it isn’t entirely clear whether that kind of determination would be binding on Mueller—“should not be pursued” is something short of “shall not be pursued.” But Mueller’s own team acknowledged in court that if the special counsel were to disobey an order from the acting attorney general, that would constitute “good cause” for firing him. So Mueller can only defy orders until the point the acting attorney general is prepared to fire him over it.

According to the regulations, should the attorney general determine that an action is so inappropriate that it must not be pursued, he or she has to report that to Congress along with the justification. Such a report, however, is not required until the “conclusion of the Special Counsel’s investigation,” so this oversight protection is unlikely to be helpful in the short term.

Put simply, if someone in Whitaker’s new role wants to create big problems for Mueller, he has ample tools to do so.

But there is another player in this dynamic: Mueller. The special counsel has so far used silence as a strategic weapon. He has chosen to act as a traditional, tight-lipped prosecutor, speaking only through indictments and criminal complaints. He has said almost nothing else in public, and his staff has not leaked. One consequence of that course is that if Mueller were to say anything publicly, his voice would be enormously powerful. He has the capacity to issue a statement, hold a news conference or even to issue a strongly worded letter of resignation. One of the key moments in the Saturday Night Massacre was when Archibald Cox, having been removed, issued a statement through his spokesman, James Doyle, who held a press conference after the Special Prosecutor's Office was shut down. If Mueller believes his investigation is being impeded, his most important tool may be the ability to say so publicly.

To an extent, Mueller has protected himself already by distributing key elements of his investigation. As the probe has matured over time, the special counsel’s office—and Rosenstein, in his role as acting attorney general for the purposes of the Russia investigation—has chosen to spin off aspects of the investigation to independent components overseen by different entities in the Justice Department. Most prominently, the investigation into Trump’s former personal lawyer Michael Cohen reportedly began with Mueller but was referred to the U.S. Attorney’s Office for the Southern District of New York. (There is also a related state-level investigation by the New York attorney general into the Trump Organization, sparked by the Cohen probe.) There are also the cases against accused Russian spy Maria Butina and alleged troll-farm accountant Elena Khusyaynova, both investigations into alleged Russian election interference conducted by U.S. attorneys in conjunction with the Justice Department’s National Security Division.

The result of this distribution is that firing Mueller would not eliminate the investigations into the president, his associates and Russian interference in U.S. elections.

Mueller has had a long time to prepare for this moment, and he may have more up his sleeve. Trump, after all, has been signaling his intention to get rid of Sessions, Rosenstein or both for many months. He has even signaled interest in putting Whitaker in charge of the probe. Shocking as Sessions’s departure is, it is not surprising. And Mueller will not have been surprised. He will no doubt be prepared.

Mueller has one more tool that we know of: Christopher Wray. Wray and Mueller have worked together before in the Justice Department under President George W. Bush. Wray, despite the circumstances of his appointment as FBI director, has shown himself to be serious about the responsibilities of the job, and he has reportedly threatened resignation over White House interference in law enforcement at least once before. It is not out of the question that he might do so again—or carry out the threat—should the integrity of the Mueller investigation be endangered.

Congress has tools as well. Writing on Twitter, New York Times reporter Maggie Haberman noted:

Trump allies are deeply perplexed by his move against Sessions, given that it all but guarantees an investigation by House judiciary. — Maggie Haberman (@maggieNYT) November 7, 2018

Trump would face no serious threat of investigation if not for the incoming Democratic majority in the House of Representatives. Given the election results, Trump is poking a bear that is already agitated. The Congress taking office in January 2019 is already inclined to hold the president to account. So Wednesday’s move is an especially aggressive poke. Incoming House Judiciary Committee Chairman Jerrold Nadler has already promised an investigation of Sessions’s removal. Incoming House Oversight Committee Chairman Elijah Cummings denounced Whitaker’s role overseeing Mueller as “wholly inappropriate” and asked the Justice Department to prepare documents on the matter for a future congressional inquiry. And incoming House Intelligence Committee Chairman Adam Schiff stated that, “If the President seeks to interfere in the impartial administration of justice, the Congress must stop him.”

The other house of Congress also has a role to play, though it is much less clear that its members are eager to play that role. Democratic senators, including Minority Leader Chuck Schumer, have called for Whitaker’s recusal. But Senate Majority Leader Mitch McConnell shored up his Republican majority in the midterm elections, and the death of Sen. John McCain and the looming departure of Sen. Jeff Flake—two of the stronger Republican voices criticizing Trump’s incursions against the rule of law—mean that McConnell’s caucus as a whole is friendlier toward the president and less likely to retaliate over Sessions’s removal. Republican Sens. Chuck Grassley and Lindsey Graham are backtracking from statements they made within the last year in opposition to Sessions’s firing. Grassley had previously declared that he would not schedule a confirmation hearing for another attorney general if Sessions were fired, but he now says that he may have time after all. Graham, who once said that there would be “holy hell to pay” if Sessions were fired, now says that Trump has a right to pick a new attorney general after the midterms and that he doesn’t buy the claim that the only way to protect Mueller is to keep Sessions around.

There are a few voices of dissent: Soon-to-be Sen. Mitt Romney announced that “it is imperative that ... the Mueller investigation proceeds to its conclusion unimpeded.” Sen. Susan Collins said that “Mueller must be allowed to complete his work without interference.” Sen. Lamar Alexander allowed that the president should be able to pick a new attorney general but insisted that “no new Attorney General can be confirmed who will stop [the Russia] investigation.” But it is not clear how many senators will actually risk anything to protect the integrity of the investigation, or the department more generally.

This brings us to the longer-term issue raised by Sessions’s firing: Who will serve as attorney general, and will the Senate demand a figure actually committed to the rule of law and to the apolitical conduct of law enforcement and counterintelligence investigations?

The key question is whether enough Republican senators agree with Alexander that they can collectively exert some influence on whomever Trump selects to permanently succeed Sessions—or if they would vote to stop an unacceptable nominee. Political pressure on Trump over his choice for FBI director in the wake of the Comey firing pushed the president to select Wray, a choice of a experienced professional without a strongly political bent, over more divisive and partisan figures like Rep. Trey Gowdy and Sen. John Cornyn. At his confirmation hearing, Wray promised to lead the FBI independently, lessening fears that the White House could act through him to control law enforcement. The same could happen here—if a portion of the Republican majority in the Senate works with Democrats to make clear that this is essential to the nominee’s winning confirmation.

There is another example to keep in mind. During his confirmation hearing to serve as President Richard Nixon’s attorney general, Elliot Richardson promised the Senate that he would not dismiss Special Prosecutor Archibald Cox for anything other than “extraordinary improprieties.” That promise eventually led him to resign, rather than obey Nixon’s order to fire Cox. A strong-minded Senate could extract similar commitments from whomever is nominated as Sessions’s successor, potentially limiting the president’s ability to interfere with the conduct of the probe.

In short, the situation Trump has concocted is genuinely dangerous, but a variety of actors have the capacity to mitigate the danger. One of those people is Whitaker himself. Whitaker has offered no basis for confidence that he will act appropriately. And Trump’s attraction to him no doubt has its roots in Trump’s own apparent conviction that Whitaker—unlike Sessions—will serve the president’s personal interests in office. That said, Sessions was not an individual whose history gave much basis for confidence that he would act honorably with respect to the Russia investigation. He came into office having been formally associated with the Trump campaign and having personally met with the Russian ambassador to the United States and then testified inaccurately on the subject at his confirmation hearing. Yet Sessions—at great personal cost—in the end put his duty as attorney general, his oath of office, before his loyalty to his boss.

When Matt Whitaker made his remarks on the investigation, he was a private citizen who had not been briefed on the investigation. Now he has taken his oath of office and he will be briefed on the investigation in detail. These are solemn realities that should have an impact. The question is whether they will.