On Friday, September 14, 2018, the moment special counsel Robert Mueller had been waiting for so long had finally happened. That day, former Trump campaign chair Paul Manafort appeared in a Washington DC court and pleaded guilty to a reduced set of charges. As part of his plea deal with Mueller’s team, Manafort agreed to cooperate with the investigation. The new deal will stave off a second trial for Manafort in a DC court which was supposed to begin this month as well as dismissing 10 mistrial counts from his trial in Virginia from August. Much of Manafort’s money and property will also be subject to forfeiture. In advance to Manafort’s fateful court appearance, Mueller’s team filed a new document that drops some charges and lays out what Manafort will admit to. He pleaded guilty to one count of conspiracy against the United States (related to his foreign lobbying work in Ukraine and his finances), and one count of conspiracy to obstruct justice (related to attempted witness tampering early this year).

Paul Manfort’s flip is enormously important for the Russia investigation since this deal marks the end of one phase in the Mueller investigation. Since his appointment in the summer of 2017, Robert Mueller has focused more on his office’s activity on Manafort than any other individual and was its most visible activity so far. He indicted the former Trump campaign chair on 25 charges in 3 separate batches and across 2 venues. In the first trial stemming from his probe, Mueller’s team got Manafort convicted on 8 counts and facing a years-long prison sentence. While investigating Russian interference with the 2016 campaign is Mueller’s main task with the Russia probe, the charges were mainly about Manafort’s past unregistered foreign lobbying work and his finances. Mueller hasn’t publicly explained his strategy. But many have long speculated that the special counsel’s main aim with charging Manafort with financial and lobbying crimes was to pressure him to “flip” so he’d agree to provide information related to their true concern of whether the Trump campaign conspired with Russia to interfere with the 2016 election.

Robert Mueller’s team initially indicted Paul Manafort in October 2017 alongside his longtime right-hand man Rick Gates on conspiracy, undeclared foreign lobbying, financial, and other crimes. Though we know Mueller had investigated Manafort’s involvement in Russian interference with the 2016 campaign, the indictment was about years’ worth of lobbying work the pair did for Ukranian politicians and government leaders prior to the campaign and what they did with their money afterward. At first, both pleaded not guilty. Then in February 2018, Mueller filed a new set of charges against the pair, again related to the Ukranian money. This spurred the younger and less wealthy Gates to strike a deal agreeing to cooperate against Manafort and pleading guilty to a reduced set of charges. But Manafort held out. 4 months later, Mueller’s team added a new allegation against him that he and a Russian associate named Konstatin Kilimnik encouraged a likely witness in his upcoming trial to stick to a false story. The new charges led Judge Amy Berman Jackson fining that Manafort had violated his conditions of release and ordering him jailed (as he has been since). During the Virginia trial, Gates testified against his former boss along with an array of other witnesses. And while Manafort’s team managed to get one holdout juror to vote against conviction of 10 charges, Mueller won a unanimous conviction on 8 others. Now with a conviction in the books and Manafort set to face a likely prison sentence, he was still facing another trial in Washington and potentially a second if Mueller retried the Virginia mistrial counts, Manafort eventually came to the table and agreed to cooperate.

Now that Paul Manafort has flipped, what does he know about the collusion or conspiracy between the Trump team and the Russian government during the 2016 campaign? Previously, Manafort has said nothing, stating that no collusion happened so he’d naturally have no information to provide. But given his intense focus on the former Trump campaign chair, Robert Mueller has long believed otherwise. And there are 2 suspicious circumstances during the 2016 campaign that we know Manafort was involved in.

The Trump Tower Meeting: Remember the infamous Trump Tower meeting that Donald Trump Jr. set up in June 2016 with a Russian lawyer and other Russia-tied figures? Well, the 3 Trump figures in attendance were Trump Jr., Jared Kushner, and Paul Manafort. Until Manafort’s flip, no attendee has become a cooperator for Mueller. Perhaps the special counsel thinks more remains to be learned about the meeting and hopes Manafort will tell them about it.

As far as we know, Paul Manafort is the first person who attended the infamous Trump Tower meeting in July 2016 who’s agreed to cooperate with Robert Mueller’s probe. We all know it arose after British publicist Rob Goldstone emailed Donald Trump Jr. to say that the Russian government had dirt on Hillary Clinton and that he could arrange a meeting to discuss its transfer with the Trump campaign. Trump Jr. infamously replied, “If it’s what you I say I love it.” Aside from Trump Jr., Manafort, and Jared Kushner, other attendees included a Russian lawyer named Natalia Veselnitskaya, real estate developer Ike Kaveladze, and lobbyist Rinat Akhmetshin, all of whom have Kremlin ties to varying degrees. Given that Manafort was Trump’s campaign manager at the time while Kushner was a significant Trump campaign figure sat in, it’s suggested the meeting was a high-level thing.

So far all of the attendees who’ve publicly spoken about it have insisted that nothing of note happened at the meeting. However, while there isn’t enough information one way or another, Goldstone’s emails setting up the meeting suggest collusion between Russia and the Trump campaign is possible. And that the Trump campaign was at least open to the idea.

Robert Mueller is keenly interested in the Trump Tower meeting since his team has requested documents about it and quizzed witnesses on what actually happened. Now he has access to someone who has no incentive to stick to the party line. Since Paul Manafort has agreed to fully cooperate, he could officially tell us whether the official story about the meeting is true. Or whether it’s a cover for a much more significant interaction that might prove that the Trump campaign colluded with Russia after all. Another question Manafort could help answer is who knew about the meeting such as Donald Trump and the Russia government. Manafort knows what went on at the meeting and what it was for as well as possibly the cover-up afterward.

Oleg Deripaska and Konstantin Kilimnik: Even more suspicious are Paul Manafort’s surreptitious contacts with 2 Russian nationals during the campaign. One is his former client Oleg Deripaska, a Russian oligarch to whom Manafort was heavily indebted. The other is Manafort’s longtime business associate Konstantin Kilmnik, who Mueller’s team has said is tied to Russian intelligence. Just weeks after joining the Trump campaign, Manafort appeared to see an opportunity. In early April, he emailed Kilimnik about his newly high media profile, writing “How do we use to get whole,” and “Has OVD operation seen?” (OVD is Deripaska’s initials). In July 2016, Manafort and Kilimnik exchanged emails about Deripaska again. Kilimnik wrote, “I am carefully optimistic on the issue of our biggest interest. He will be most likely looking for ways to reach out to you pretty soon.” Manafort replied that if Deripaska, “needs private briefings we can accommodate.” As the summer wore on, the pair’s emails on the topic grew vaguer. In late July, Kilimnik wrote to Manafort, “I met today with the guy who gave you your biggest black caviar jar several years ago. We spent about 5 hours talking about his story, and I have several important messages from him to you.” Again, this is believed to be about Deripaska with “caviar” meaning money. Kilimnik and Manafort arranged to meet in New York City on August 2 for Kilimnik had “long caviar story” to tell and “several important messages.” Days after the meeting, Deripaska took a yacht trip with Russian deputy prime minister Sergei Prikhodko who’s focused on foreign policy. All this occurred while Manafort chaired the Trump campaign before his mid-August 2016 firing. Since he’s based in Moscow, Kilimnik is unlikely to face charges.

Nonetheless, we still don’t know what happened between Manafort, Kilimnik, and Deripaska during the campaign. Maybe this is where the Trump/Russia collusion happened. Maybe Manafort was just freelancing and trying to get himself paid and it doesn’t involve Donald Trump personally. Yet, it’s one of the biggest loose ends about what happened in 2016. But whatever the case, Manafort has committed to tell Mueller the truth.

Paul Manafort’s guilty plea doesn’t say anything about possible collusion between the Trump campaign and Russia military intelligence officials who’ve allegedly attacked the 2016 election for Donald Trump’s benefit. But the plea agreement’s implications point to many ways Manafort’s decision could legal and politically damage Trump. Trump’s constant assertion that the Mueller probe is a “witch hunt” has only sought to bring down “innocent” men keeps weakening when each “innocent” man confesses to federal felonies. While Trump claims the investigation is a money pit, Manafort’s asset surrender of accounts and properties worth millions of dollars shows that the Mueller probe has basically paid for itself. Furthermore, Manafort’s guilty plea virtually blocks any avenue Trump can obstruct the investigation by pardoning him. Now that Manafort has agreed to cooperate with Mueller and Trump has no apparent way to learn what his former campaign chair has told prosecutors or a grand jury, there’s no way Trump can benefit with a pardon attempt. Finally, after months of painting Manafort as a “good guy” who’s been treated “unfairly,” Trump’s spin doctors will have to reverse course on a potential witness against their guy. Rudy Giuliani seemed confused about this fact, releasing a statement saying, “the president did nothing wrong and Paul Manafort will tell the truth,” before retracting the part about Manafort.

Furthermore, what Paul Manafort knows is important for several threads of the Russia investigation like the hack on the DNC, any communication between the Trump campaign and Russian interests, and most importantly, the infamous 2016 Trump Tower meeting. Before striking the plea deal with the former campaign chair, prosecutors sat down with Manafort for a proffer session where a defendant answers from investigators, including details about their own case and other criminal activity they might’ve witnessed. Ultimately, prosecutors will only agree to a cooperation deal with a defendant if the latter gives them information that other witnesses and documents can verify. So Mueller’s team feels that what Manafort knows is really critical evidence about that Trump Tower meeting, who knew about it and when, and what other contacts took place between the campaign and people around Donald Trump.