Robert Mueller first dropped Paul Manafort into the criminal-justice system last October, and he’s been tightening the vise ever since. The special counsel has flipped Manafort’s close associates and used their testimony against him. He persuaded a judge to revoke Manafort’s house arrest and send him to jail for trying to tamper with other witnesses. And he made a convincing enough case for a jury to find Manafort guilty on eight fraud-related counts in last month’s trial in Alexandria, Virginia, all but guaranteeing the 69-year-old political operative a hefty prison sentence.

On Friday, Manafort finally cracked from the pressure. President Donald Trump’s former campaign chairman pleaded guilty to conspiracy against the United States and conspiracy to obstruct justice in a D.C. courthouse. He also admitted his guilt to ten charges on which the Alexandria jurors failed to reach a verdict. And in exchange for a lighter sentence to be determined later, Manafort gave Mueller his prize after eleven months of labor: a binding agreement to “cooperate fully, truthfully, completely and forthrightly ... in any and all matters as to which the government deems the cooperation to be relevant.”

This is the moment that Trump feared and tried to prevent. Manafort is one of the few people who can provide details about the extent of the campaign’s interactions with the Russian government during the last election. His extensive connections to Moscow-aligned figures in Eastern Europe make him the likeliest vector for whatever conspiracy may have existed between the Trump campaign and the Kremlin to sabotage Hillary Clinton’s presidential bid in 2016. Manafort’s cooperation will likely shed new light on key moments during that fateful year: He’s the only American, for example, who participated in the infamous Trump Tower meeting in June 2016 that isn’t related to Trump by blood or by marriage. Friday’s plea agreement could therefore increase the legal peril not only for the president, but also for his inner circle and members of his family who have already testified about the encounters.

Manafort’s guilty plea spares him from the financial and legal ordeal of facing a second trial in D.C. that was scheduled to begin later this month. The first charge relates to his work as a political consultant for pro-Kremlin political parties in Ukraine, where he amassed a small fortune and illegally funneled it back into the United States. “Manafort laundered more than $30 million to buy property, goods, and services in the United States, income that he concealed from the United States Treasury, the Department of Justice, and others,” the indictment said. “Manafort cheated the United States out of over $15 million in taxes.”

The second charge against Manafort is connected to his communications with other former conspirators earlier this year. According to the indictment, Manafort reached out to his associates, including Konstantin Kilimnik, a former business associate reportedly connected to the Russian intelligence services, to coordinate their testimony on matters related to his overseas work. Mueller first charged Manafort over this action—attempting to undermine the investigation—in June, which led a federal judge to revoke the 69-year-old lobbyist’s house arrest and let him await trial in jail.

The result is perhaps Mueller’s most important victory yet, and a vindication of his quiet, patient strategy in the investigation. Federal prosecutors in white-collar and organized-crime cases often begin by bringing charges against low-level members, often on unrelated charges. Investigators then work their way up the chain of command by offering leniency in exchange for cooperation and testimony against higher-level conspirators. Mueller has maintained the radio silence of a Soviet submarine captain since taking over the investigation last spring, but his prosecutions so far suggest that he’s employing a similar strategy against Trump and his associates.

What distinguishes Trumpworld from an organized-crime syndicate or a money-laundering bank, of course, is the presidency itself. Trump could use its powers to shut down the Russia investigation, fire Mueller and other top Justice Department personnel, and pardon his cronies with relative ease. That threat is now somewhat mitigated. Mueller’s team told the court during Friday’s allocution that Manafort had already begun providing them with information, which limits the practical impact of pardoning him now.

Moreover, in recent months, the president’s legal team occasionally suggested they might demand Mueller hew to a September 1 deadline, implying any major action after that would be interfering the November midterms. If Trump now attempts to halt Manafort’s cooperation with a pardon or other major move, he may face a similar quandary. Democrats are currently forecast to make major gains in the House of Representatives and have a slim chance at retaking the Senate. Given Mueller’s current popularity, any substantive steps against him would probably make a Democratic takeover of Congress—and with it, potential impeachment proceedings—even more likely. Manafort’s flip means Trump is damned if he tries to stop the Russia investigation before November and damned if he doesn’t.

It’s theoretically possible, of course, that Trump played no part in any possible collusion, and that Manafort doesn’t know anything that could implicate him. The president, like all potential defendants, is legally innocent until he’s proven guilty.

Trump and his allies, however, aren’t acting like innocents. Earlier this year, I wrote that the best available explanation for Mueller’s quiet moves and Trump’s noisy countermoves is that the president knows or believes that the special counsel can prove collusion. Many of the president’s most vociferous defenders operate under the assumption that Trump is guilty but Mueller won’t or shouldn’t find any proof.

Trump’s posture towards the investigation supports this view as well. After the twin blows last month of Manafort’s conviction in Virginia and Michael Cohen’s guilty plea in New York, the president praised his former campaign chief for not bending the knee to prosecutors. “I feel very badly for Paul Manafort and his wonderful family,” Trump wrote on Twitter. “[The Justice Department] took a 12 year old tax case, among other things, applied tremendous pressure on him and, unlike Michael Cohen, he refused to ‘break’—make up stories in order to get a ‘deal.’ Such respect for a brave man!”

Shortly thereafter, Trump reportedly told a Fox News reporter off camera that he was considering a pardon for Manafort. He then suggested in the interview that “flipping,” a common prosecutorial tactic, “should be illegal.” Rudy Giuliani, the president’s personal attorney, quickly briefed reporters that Trump and his legal team agreed that there would be no pardons until after Mueller’s investigation had ended. The implicit message seemed to be clear: As long as Manafort stays quiet, the president will spare him from prison when this all blows over.

That option now seems moot. It’s not clear what the president’s countermove will be. The White House’s only public response so far is to stress that Manafort’s legal troubles don’t directly affect them. “This had absolutely nothing to do with the President or his victorious 2016 Presidential campaign,” White House Press Secretary Sarah Huckabee Sanders told reporters on Friday. “It is totally unrelated.” Left unspoken were the two most important words: for now.