WASHINGTON — Paul J. Manafort was in bed early one morning in July when federal agents bearing a search warrant picked the lock on his front door and raided his Virginia home.
They took binders stuffed with documents and copied his computer files, looking for evidence that Mr. Manafort, President Trump’s former campaign chairman, set up secret offshore bank accounts. They even photographed the expensive suits in his closet.
The special counsel, Robert S. Mueller III, then followed the house search with a warning: His prosecutors told Mr. Manafort they planned to indict him, said two people close to the investigation.
“They are setting a tone. It’s important early on to strike terror in the hearts of people in Washington, or else you will be rolled,” said Solomon L. Wisenberg, who was deputy independent counsel in the investigation that led to the impeachment trial of President Bill Clinton in 1999. “You want people saying to themselves, ‘Man, I had better tell these guys the truth.’”
Mr. Manafort is under investigation for possible violations of tax laws, money-laundering prohibitions and requirements to disclose foreign lobbying. Michael T. Flynn, the former national security adviser, is being scrutinized for foreign lobbying work as well as for conversations he had last year with Russia’s ambassador to the United States. On Monday, Mr. Flynn’s siblings announced the creation of a legal-defense fund to help cover their brother’s “enormous” legal fees.
But associates of both Mr. Manafort and Mr. Flynn have received more peremptory treatment. Instead of invitations to the prosecutor’s office, they have been presented with grand jury subpoenas, forcing them to either testify or take the Fifth Amendment and raise suspicions that they had something to hide. At least three witnesses have recently been subpoenaed to testify about Mr. Manafort:
Jason Maloni, a spokesman who appeared before the grand jury for more than two hours on Friday, and the heads of two consulting firms — Mercury Public Affairs and the Podesta Group — who worked with Mr. Manafort on behalf of Viktor F. Yanukovych, the pro-Russia former president of Ukraine.
Mr. Mueller’s team also took the unusual step of issuing a subpoena to Melissa Laurenza, a specialist in lobbying law who formerly represented Mr. Manafort, according to people familiar with the subpoena. Conversations between lawyers and their clients are normally considered bound by attorney-client privilege, but there are exceptions when lawyers prepare public documents that are filed on behalf of their client.
“They seem to be pursuing this more aggressively, taking a much harder line, than you’d expect to see in a typical white-collar case,” said Jimmy Gurulé, a Notre Dame law professor and former federal prosecutor. “This is more consistent with how you’d go after an organized crime syndicate.”
The tactics reflect some of the hard-charging — and polarizing — personalities of Mr. Mueller’s team, seasoned prosecutors with experience investigating financial fraud, money laundering and organized crime.
Some lawyers defending people who have been caught up in Mr. Mueller’s investigation privately complain that the special counsel’s team is unwilling to engage in the usual back-and-forth that precedes — or substitutes for — grand jury testimony. They argue that the team’s more aggressive tactics might end up being counterproductive, especially if some grand jury witnesses turn out to be more guarded than they would have been in a more informal setting or invoke the Fifth Amendment.
The longer Mr. Mueller’s investigation goes on, the more vulnerable he will be to allegations that he is on a fishing expedition, said Katy Harriger, a professor of politics at Wake Forest University and the author of a book on special prosecutors. Such accusations dogged the investigation of Kenneth W. Starr, the independent counsel whose investigation of Mr. Clinton stretched on for years.
To a degree, Mr. Mueller is in a race against three congressional committees that are interviewing some of the same people who are of interest to the special prosecutor’s team. Even if the committees refuse to grant them immunity, congressional testimony that becomes public can give other witnesses a chance to line up their stories.
Rep. Adam Schiff of California, the top Democrat on the House Intelligence Committee, said committee staff members were going to great lengths not to get in Mr. Mueller’s way. But Senator Charles E. Grassley, the chairman of the Senate Judiciary Committee, indicated last week that his committee might subpoena witnesses to testify about the circumstances of Mr. Comey’s firing even over Mr. Mueller’s objections.
Mr. Mueller’s need to navigate this complex landscape could explain the timing of the raid on Mr. Manafort’s house, which took place in the early hours of July 26. The raid came one day after Mr. Manafort was interviewed by staff members of the Senate Intelligence Committee.
On the day of the raid, Mr. Manafort was scheduled to talk to the Senate Judiciary Committee, an interview that was eventually canceled.
It is unusual for a prosecutor to seek a search warrant against someone who, like Mr. Manafort, had already put his lawyer in contact with the Justice Department. No search warrants were executed during the investigations by Mr. Starr or Patrick J. Fitzgerald, a special counsel appointed during the George W. Bush administration to investigate the leak of the name of a C.I.A. officer.
T
o get the warrant, Mr. Mueller’s team had to show probable cause that Mr. Manafort’s home contained evidence of a crime. To be allowed to pick the lock and enter the home unannounced, prosecutors had to persuade a federal judge that Mr. Manafort was likely to destroy evidence.
Said Mr. Gurulé, the former federal prosecutor, “
Clearly they didn’t trust him.”