President Trump has howled in all caps for nearly a year as the Justice Department has delved deeper and deeper into his orbit. Special counsel Robert S. Mueller III indicted his former campaign chairman. Then he secured a guilty plea from his former national security adviser. All the while, Mueller and his investigators have spent hours questioning White House officials about whether the president had sought to obstruct justice.

But the FBI’s seizure on Monday of privileged communications between Trump and his private lawyer, Michael D. Cohen — as well as documents related to a $130,000 payment to Stormy Daniels, the adult-film actress who has alleged a sexual affair with Trump — was a particularly extraordinary move that opens a whole new front in the converging legal battles ensnaring the administration.

Cohen is Trump’s virtual vault — the keeper of his secrets, from his business deals to his personal affairs — and the executor of his wishes.

“This search warrant is like dropping a bomb on Trump’s front porch,” said Joyce White Vance, a former U.S. attorney in Alabama.

Mark S. Zaid, a Washington lawyer, said the seizure of Cohen’s records “should be the most concerning for the president.”

“You can’t get much worse than this, other than arresting someone’s wife or putting pressure on a family member,” he said. “This strikes at the inner sanctum: your lawyer, your CPA, your barber, your therapist, your bartender. All the people who would know the worst about you.”

The president spent much of Monday afternoon glued to the television. Aides said Trump watched cable news coverage of surprise raids on Cohen’s Manhattan office, home and hotel room by FBI agents, who took the lawyer’s computer, phone and personal financial records after a referral from Mueller.

As the sun began to fall in Washington, Trump offered reporters his initial reaction: “It’s a disgraceful situation.”

“I have this witch hunt constantly going on,” Trump said. “That is a whole new level of unfairness,” he added, leaving no doubt that he views Monday’s actions as a personal affront. Trump called Cohen “a good man” and went on to criticize Attorney General Jeff Sessions, saying he had made “a very terrible mistake for the country” by recusing himself from the Russia probe.

Asked why he had not fired Mueller, Trump left the door open. “We’ll see what happens,” he told reporters. “Many people have said, ‘You should fire him,’ ” the president added.

Shortly after the raids began Monday morning, Trump received a heads-up at the White House. He huddled in the Oval Office with Ty Cobb, the White House lawyer who oversees its handling of the Mueller probe, as well as with White House counsel Donald McGahn and White House Chief of Staff John F. Kelly, officials said.

Other aides said they did not understand what was happening and struggled to pinpoint the significance of the seizures. Many officials sought to keep their distance from the developments, deferring comment until a strategy was determined.

Michael D. Cohen, personal attorney for President Trump, arrives at Trump Tower in New York on Jan. 17. (Stephanie Keith/Reuters)

Aides said they viewed Trump’s late-afternoon comments to reporters as a necessary venting session. He had been grousing privately about Deputy Attorney General Rod J. Rosenstein, a Trump appointee who oversees the Mueller investigation because of Sessions’s recusal.

He complained about Rosenstein again Monday in private, a White House adviser said, and stewed all afternoon about the warrant to seize Cohen’s records, at times raising his voice. Trump said that…