WASHINGTON — Even though the final report from the Republican-led House Intelligence Committee will find no evidence of collusion between the Trump presidential campaign and Russia, a new study by a Democratic-aligned advocacy group suggests the committee didn’t look very hard.

According to the Center for American Progress’s Moscow Project, the House committee charged with investigating Russian involvement in the 2016 election obtained either no or incomplete information about 81 percent of the known contacts between Trump officials and Russians, or groups and individuals with strong Russia ties like Wikileaks.

Those officials include former national security adviser Michael Flynn, who has pled guilty to lying to the FBI, and former campaign manager Paul Manafort, who has been indicted on an array of tax, financial, and bank fraud crimes and has worked on behalf on foreign entities aligned with Russia.

Another key finding, according to CAP’s examination: At least 22 high-ranking Trump campaign officials knew about the contacts during the 2016 campaign and the transition.

CAP's Moscow Project is a research initiative aimed at documenting Trump’s Russia ties.

The report, provided to NBC News, comes as the committee is due to vote Thursday on its final report and effectively end its investigation. Committee Democrats disagree with its conclusions and have accused Republicans of prematurely shuttering the probe.

Based on news reports, public statements, witness lists and indictments related to special counsel Robert Mueller’s investigation, the CAP report documents at least 70 contacts between the Trump team and Russia-linked operatives, from January 2016 through 2017 as Trump took the oath of office. They include 22 meetings, including Skype calls.

While many news organizations, including NBC, have documented the timeline and large volume of contacts between Trump officials and the Russians, the CAP report is particularly comprehensive, making some connections that have not been widely reported and taking an exhaustive view of how many Trump officials were aware of the regular interactions.

And the 12-page study claims that the committee failed to interview key witnesses involved in 60 percent of the cases.

In addition to Manafort and Flynn, these include George Papadopoulos, the Trump campaign foreign policy aide whose boast about Russia having “political dirt” on Hillary Clinton sparked an FBI probe; and Anthony Scaramucci, the onetime White House communications director who criticized U.S. sanctions on Russia after a January meeting in Davos, Switzerland, with Kirill Dmitriev, a Kremlin ally and the head of a sanctioned Russian investment fund.

A spokeswoman for Rep. Mike Conaway, R-Texas, who presided over the investigation, said the committee could no longer call Manafort and Flynn after they were charged or pleaded guilty in the special counsel’s investigation.

Conaway has said that dozens of interviews and a review of intelligence agencies' findings suggests the Russian goal was more to sow confusion and discord than it was to help Trump. That is at odds with the U.S. intelligence community, which said the Kremlin was clearly trying to help Trump.

The House probe is shutting down as new information is coming to light about Cambridge Analytica, the data firm with ties to Trump’s campaign, that could weigh in a collusion investigation.

“For months we urged the majority to bring in other witnesses from Cambridge Analytica and the Trump campaign digital media operation, but they were unwilling to do so,” said Rep. Adam Schiff of California, the committee’s top Democrat. "We now see the severe consequences of their failure to do so."

Alexander Nix, Cambridge Analytica’s CEO, was suspended this week after he was secretly recorded talking about deceptive methods employed by the company, including bribery, blackmail and misinformation campaigns.

“The American people cannot rely solely on the investigative work of journalists,” Schiff said in a statement.

CAP also found that in another 21 percent of the known contacts with specific individuals, pleas from House Democrats to call back witnesses, including those who refused to answer questions, were rejected.

These include longtime Trump personal attorney Michael Cohen; Attorney General Jeff Sessions; Trump son-in-law and senior adviser, Jared Kushner; Donald Trump Jr.; and Erik Prince, a Trump supporter and founder of the Blackwater security firm.

Democrats say the committee’s refusal to dig more thoroughly into Trump associates’ dealings with Russia has emboldened the president to take a more aggressive posture toward Mueller's investigation of Trump’s Russia ties. Over the weekend, Trump began to target Mueller by name on Twitter.

According to a recent status report by Democrats on the House Intelligence Committee, more than 30 key witnesses have not been interviewed. These include personnel and contractors from the campaign’s digital operations, including Cambridge Analytica.

Particularly glaring oversights, according to the CAP report, include not asking Trump attorney Cohen for documents about a proposed 2016 Trump Tower deal in Moscow and not calling Kushner back for more information about a June 9 meeting at Trump Tower in New York with Russians, including attorney Natalia Veselnitskaya and a former Soviet counterintelligence officer and lobbyist. An email showed Trump Jr. eager to attend that meeting, where he hoped to receive information that could incriminate Hillary Clinton.

A man walks into the Center for American Progress at their office on Feb. 21, 2018 in Washington. Jacquelyn Martin / AP file

Committee Democrats also wanted to hear from Sessions on his conversations with Trump about the Russia investigations. They say Prince and another longtime Trump friend, Roger Stone, may have lied to the committee about their interactions with Russians in the Seychelles and with Wikileaks, respectively.

Days after the House Intelligence Committee announced its findings, The New York Times reported on a secret meeting in the Seychelles between Prince and a Russian close to President Vladimir Putin as part of an apparent effort to establish a back channel to the Kremlin.

While Democrats say they wanted more information from several witnesses as part of the committee probe, it is impossible to say for certain what information the committee did and did not obtain, given that there is no public access to the transcripts themselves.

While many of the individual meetings have been exhaustively covered by news organizations, the CAP report shows the interactions were regular (often with little more than days separating them) and it highlights some actors such as Ivan Timofeev, who claimed connections to the Russian Ministry of Foreign Affairs.

The interactions documented in the report begin with a January 2016 email from Trump’s personal lawyer Cohen to Putin’s top spokesperson, Dmitry Peskov, about a stalled attempt to build a Trump Tower project in Moscow.

In March there were meetings between Papadopoulos, whose actions prompted the start of an FBI probe, and both Joseph Mifsud, a Maltese academic alleged to have high-level connections to the Kremlin, and a female Russian national believed to be Putin’s relative.

The report also highlights that, following the now infamous Trump Tower meeting in June 2016, Papadopoulos had “several email and Skype exchanges” with Timofeev, who suggested a campaign official come to Russia for a meeting.

A month later, in July, Carter Page, a Trump campaign foreign policy adviser, traveled to Moscow to give a speech. There he met with Andrey Baranov, head of investor relations at Rosneft, and spoke to Russian Deputy Prime Minister Arkady Dvorkovich.

In August, Stone was in touch with Guccifer 2.0, which worked with Wikileaks to release thousands of stolen Clinton campaign emails during the election, and Manafort was corresponding with Konstantin Kilimnik, a Russian-Ukrainian political operative and former member of Russian intelligence.

By late September, Wikileaks was in touch via Twitter with Trump Jr., who agreed to its requests to push a story about Hillary Clinton and to urge his father to tweet Wikileaks links. Wikileaks contacted Trump Jr. several other times, but he stopped replying to the messages.

On Oct. 7, within hours after a lewd “Access Hollywood” tape of Trump bragging about grabbing women by their genitals surfaced, Wikileaks started dropping emails stolen from Clinton campaign chair John Podesta.

With the House investigation wrapping up, it now falls to the Senate Intelligence Committee and special counsel Mueller to fill in the blanks.

In an interview Sunday on NBC’s “Meet the Press,” Conaway misspoke about whether the committee was even tasked with examining collusion and acknowledged not having talked to a key witness, Papadopoulos.

“He got outside the opportunity for us to interview him when he was charged and got caught up in the Mueller investigation,” Conaway said. “We're trying to stay away from the Mueller investigation and not confuse that or hurt it one way or the other.”

CORRECTION (March 22, 2018, 11:45 a.m. ET): A previous version of this article misspelled the last name of a Russian-Ukrainian political operative and former member of Russian intelligence. He is Konstantin Kilimnik, not Kiliminik.