In one of the most dramatic developments in special counsel Robert Mueller’s investigation so far, the FBI has raided former Trump campaign chair Paul Manafort’s home, according to a new Washington Post report.

Before dawn on July 26, agents showed up at Manafort’s home without warning, presented a search warrant, and gathered many documents, per Post reporters Carol Leonnig, Tom Hamburger, and Rosalind Helderman.

Mueller’s investigation has been much discussed in Washington, but its work has so far mainly taken place behind the scenes. Now, though, this report gives us a very public indication that Manafort is under very serious scrutiny — and that Mueller may be suspicious that he’s not voluntarily disclosing the whole story.

Manafort has long been an obvious suspect for potential collusion between the Trump campaign and Russia, given his years of lucrative work for rich pro-Russia Ukrainian politicians and a Russian oligarch close to Vladimir Putin. He also attended the June 2016 meeting that Donald Trump Jr. set up with Russian lawyer Natalia Veselnitskaya with the hope of getting derogatory information about Hillary Clinton.

Beyond that, Manafort appears to be in legal trouble because of his curious finances (per the Wall Street Journal, he’s being looked at for money laundering) and for initially failing to register as a foreign agent for his Ukrainian work. Mueller’s team has taken over this preexisting investigation.

There’s no indication that President Trump knew of the raid, but hours after it happened, he tweeted that Attorney General Jeff Sessions should have replaced the acting FBI director.

Why didn't A.G. Sessions replace Acting FBI Director Andrew McCabe, a Comey friend who was in charge of Clinton investigation but got.... — Donald J. Trump (@realDonaldTrump) July 26, 2017