President Donald Trump’s campaign chairman Paul Manafort pleaded guilty to conspiracy against the United States and conspiracy to obstruct justice—all on top of what he’s already been convicted of in his Virginia trial. He’s also now cooperating with the Mueller investigation. There’s only one person that was above him on the campaign.

With Manafort’s cooperation agreement, Mueller is climbing the ladder and is now clearly in Trump’s inner circle:

• Mueller now has secured convictions against and reached cooperation agreements with Trump’s campaign chairman Paul Manafort, his deputy campaign chairman and deputy head of his inaugural committee Rick Gates, and his first national security adviser, Michael Flynn. Trump’s longtime lawyer and fixer Michael Cohen also pleaded guilty in a separate probe, implicated President Trump in a felony, and said he would cooperate with Mueller.
• Trump is clinging to the position that the convictions of his campaign chairman, deputy campaign chairman, lawyer, and national security adviser are not related to him. If that were true, who would they be cooperating against?
• An added benefit of Manafort’s plea deal: He agreed to forfeit to the government an estimated $46 million in assets he illegally obtained from his crimes.

The plea agreement requires cooperation “in any and all matters as to which the Government deems the cooperation relevant.” With that in mind, here’s a brief list of topics about which Mueller might like to know more:

• What were all the meetings and contacts between the Trump campaign and Russian-linked operatives about?
• Details about the June 9 meeting in Trump Tower and the circumstances leading to it.
• Details about the financing of the Trump campaign—and whether any funding came from Russia.
• Who was behind the decision to change the RNC platform in a pro-Kremlin direction?
• How did a desperate and deeply in debt Manafort first come to join the campaign, and how close was he to Trump after he officially left?
• Did he ultimately provide any information to Oleg Deripaska? If so, what? And did anybody else know about it?
• What was Roger Stone’s role with the campaign?
• And, most of all: What did Trump know, and when did he know it?

The charges against Manafort demonstrate why he was the natural choice to lead the Trump campaign: If you want to collude with Russia, it helps to have someone who has done it before.

• Manafort spread false corruption allegations against Yanukovych’s opponents in the press, capitalized on Russian propaganda efforts, and pushed his candidates to undermine NATO and the EU.
• Manafort’s right-hand man, Konstantin Kilimnik, was a Russian intelligence agent, and they were in contact throughout the campaign. Kilimnik also assisted Manafort in obstructing the Mueller investigation.
• The charges also illuminate Manafort’s motive to collude—he himself was compromised by Russia. With his biggest patron deposed and his riches hidden in inaccessible offshore bank accounts, Manafort turned to peddling access to his new employer to keep his debtors off his heels—even if that meant complicity in an unprecedented and unprovoked attack on the United States.

The Kremlin’s favorite American political operative, who also just happened to run the Trump campaign, is now cooperating with Mueller. The walls are closing in on Trump.