While Donald Trump and his surrogates were loudly campaigning against Robert Mueller on Twitter and on TV, the special counsel and his team of F.B.I. investigators has been quietly building their case, the details of which burst into public view Wednesday when The Washington Post reported that the bureau searched the home of Trump’s former campaign chairman Paul Manafort in a dramatic pre-dawn raid at the end of last month.

The raid, which occurred one day after Manafort met with the Senate Intelligence Committee, indicates that the Justice Department investigation has entered a heightened stage—and that Mueller is willing to use any investigative tools at his disposal to determine the extent of the Russian government’s interference in the presidential election.“I think it adds a shock and awe enforcement component to what until now has followed a natural path for a white-collar investigation,” Jacob Frenkel, a former federal prosecutor, told the Post. “More so than anything else we’ve seen so far, it really does send a powerful law enforcement message when the search warrant is used. . . . That message is that the special counsel team will use all criminal investigative tools available to advance the investigation as quickly and as comprehensively as possible.” (Manafort has repeatedly denied any wrongdoing.)

Manafort has provided more than 400 pages worth of documents to the various Congressional committees investigating the allegations that the Trump campaign colluded with the Kremlin to derail Hillary Clinton’s candidacy, but Mueller’s aggressive tactics suggest he thinks Manafort may not be fully cooperating with law enforcement, his assurances to the contrary. “It is a big deal,” Peter Zeidenberg, a former Justice Department prosecutor, told Politico. “Prosecutors do not take aggressive steps like this with subjects who the government feels are being open and cooperative. And they also do not do this to ‘send a message.’ They do it because they think there is evidence to be found and that if they do not act aggressively, it could be destroyed.” Senator Richard Blumenthal echoed the sentiment in a statement. “This kind of raid—in the early morning hours with no advance notice—shows an astonishing and alarming distrust for the president’s former campaign chairman. It seems to decimate his claim that he is cooperating with law enforcement,” the Connecticut lawmaker said.

Manafort, a longtime political operative and lobbyist, has reportedly been under F.B.I. scrutiny since 2014—well before Trump declared his candidacy—for work that he conducted as a political consultant for the pro-Kremlin Party of Regions in Ukraine. He resigned as Trump’s campaign chairman last August, in the wake of a New York Times report that he had been designated in a handwritten ledger to receive $12.7 million in undisclosed payments from the Ukrainian group. (Last month, Ukrainian prosecutors said they haven’t found any proof of illegal payments to Manafort.)

The former Trump staffer has repeatedly denied that he is working with the feds. But the search warrant for Manafort—which reportedly sought tax, banking and other documents—isn’t the only way the F.B.I. is building its case. On Wednesday, Politico reported that federal investigators also sought cooperation from Manafort’s son-in-law Jeffrey Yohai, with whom he has partnered on business deals. Yohai is under investigation by the U.S. attorney’s office in Los Angeles over a series of real estate deals and is reportedly facing allegations of operating a Ponzi Scheme. Bloomberg reported on Thursday that the F.B.I. has also issued subpoenas to Rick Gates, a longtime business partner of Manafort’s, for business records and is investigating the political operative’s ties to Ukrainian oligarch Dmitry Firtash, who has been charged in an unrelated bribery case and is awaiting extradition to the U.S.