On Friday Paul Manafort, former chairman of Donald Trump’s presidential campaign, pleaded guilty to two charges, conspiracy against the United States and witness tampering. The former campaign manager struck a plea deal with special counsel Robert Mueller III and will now be fully cooperating with Mueller’s team.

Manafort will now be cooperating as a potential witness and is expected to provide evidence meant to prove the Trump administration relied on Russian influence during the 2016 elections. In exchange for his cooperation, Manafort has been granted leniency in his sentence and has avoided heading into a second trial.

Given his agreement to cooperate, Manafort will now have to testify in court proceedings, hand over documents and offer interviews as well as briefings to Mueller’s office. He has also forfeited his right to have a lawyer present during said interviews. To Manafort’s benefit, he will only receive a maximum sentence of 10 years in prison.

Legal experts consider Manafort’s cooperation a major win for Mueller’s team, and a colossal concern for Trump. “Manafort’s cooperation is a tremendous achievement for the Mueller investigation—maybe the single biggest development yet. Manafort provides Mueller with an insider to the infamous June 2016 Trump Tower meeting and likely many other key moments,” explained Seth Waxman, an ex-prosecutor in Washington, D.C.

And now the question on everyone’s mind is, what does this mean for the Trump administration? Only three weeks ago, President Trump praised Manafort for refusing to cooperate with Mueller on the Russian probe.

On twitter, the President wrote, “I feel very badly for Paul Manafort and his wonderful family. ‘Justice’ 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!”

Legal experts claim Manafort’s cooperation deal promises serious legal trouble for President Trump. Former federal prosecutor Elizabeth de la Vega told The Guardian, “Manafort’s guilty plea—with cooperation!—is an absolute nightmare for Trump, and his family. Manafort essentially took over the campaign as of mid-April 2016 and was Trump’s go-to man during a critical period of the campaign.”

She later added, “Reporting shows that Trump called Manafort 20 times a day and, of course, Manafort knows the whole story of the Trump Tower meeting and events before and after.”

President Trump’s lawyer, Rudy Giuliani, was quick to respond to news of Manafort’s plea deal. On Saturday he tweeted, “According to sources close to Manafort defense: ‘The cooperation agree does not involve the Trump campaign…There was no collusion with Russia’.” Giuliani tried to distance President Trump from the special counsel’s investigation once again, claiming nothing would surface from Manafort’s cooperation.

Manafort is the sixth person to plead guilty as a result of the Mueller investigation, following Michael D. Cohen, Sam Patten, Rick Gates, Richard Pinedo, and Michael T. Flynn. Mueller’s team have also sentenced Alex van der Zwaan and George Papadopoulos to prison.