WASHINGTON — Andrew G. McCabe has risen so fast at the F.B.I. that he has become a source of both admiration and resentment. So a favorite way to criticize him is to offer one of the most backhanded compliments in the bureau’s lexicon: He’s a great briefer.
Mr. McCabe’s talent for briefing his superiors is regarded by many workaday agents as nothing more than an ability to discuss somebody else’s work. But it is highly valued at F.B.I. headquarters, and in a city where briefings become policy.
“With McCabe, it was always his capacity to understand an issue at great depth that made him stand out,” said James W. McJunkin, who supervised Mr. McCabe years ago in the F.B.I.’s counterterrorism division. Mr. McCabe provided unvarnished information, he said, with cut-to-the-chase precision.
That ability was on display on Thursday in Mr. McCabe’s first public appearance as acting director, less than 48 hours after President Trump fired James B. Comey, Mr. McCabe’s boss.
In testimony before the Senate Intelligence Committee, Mr. McCabe, 49, crisply refuted a pair of Trump administration assertions about Mr. Comey’s firing.
The White House said Mr. Comey had lost the support of his agents. Not so, Mr. McCabe said.
The White House said the F.B.I. regarded the investigation into Russian election interference as a low priority. Mr. McCabe called it “highly significant.”
Mr. McCabe’s standing up to a temperamental president who has repeatedly smacked the bureau like a political piñata won over at least some F.B.I. agents who had viewed Mr. McCabe as overly cautious. Mr. Trump has described the agency as corrupt, repeatedly belittled Mr. Comey and called the F.B.I. investigation into Russian influence in the 2016 election and potential collusion with the president’s associates a “hoax.”
Senator Martin Heinrich, Democrat of New Mexico, said he was surprised by Mr. McCabe’s bluntness. “I wasn’t expecting it,’’ he said in an interview. “It was pleasantly candid. He bucked the system.”
While many F.B.I. agents try to chart career paths out in the field by making cases and arrests — and avoiding the politics of Washington — Mr. McCabe has stayed here and thrived. He sometimes comes off at the F.B.I. as rigid, particularly in comparison with the more outgoing Mr. Comey. But Mr. McCabe, a triathlete known for biking 35 miles to work from Virginia, has stood out for his intellect and the range of high-profile cases he has been at the center of.
In his previous jobs at the F.B.I., Mr. McCabe was deeply involved in the investigation of the 2013 Boston Marathon bombing and the arrest and interrogation of Ahmed Abu Khattala, a suspect in the 2012 attacks on the American compounds in Benghazi, Libya. As deputy director, he has been steeped in the Russia investigation that has so frustrated Mr. Trump and the White House.
A graduate of Duke and Washington University School of Law in St. Louis, Mr. McCabe joined the F.B.I. in 1996, and he worked as an organized crime investigator in New York, where he was also a member of a SWAT team.
“Anybody who is a detractor of McCabe’s career probably has a few holes in their professional portfolio,”
said James A.
Gagliano, who supervised him on that team. “There are a handful of guys I can attribute this to: His character is unimpeachable.”
Before the president fired Mr. Comey, the F.B.I. director was under investigation by the Justice Department’s inspector general for the decisions he made regarding the investigation into Hillary Clinton’s use of a private email server. The inspector general was also looking at whether Mr. McCabe should have recused himself from any involvement in that investigation.
In 2015, Mr. McCabe’s wife, Jill McCabe, ran for a State Senate seat in Virginia as a Democrat and accepted nearly $500,000 in contributions from the political organization of Gov. Terry McAuliffe, a longtime friend of the Clintons. Though Mr. McCabe did not become deputy director until February 2016, months after his wife was defeated, critics within and outside the agency said he should have recused himself.
Mr. McCabe has said he told his superiors about his wife’s candidacy and sought ethics advice from F.B.I. officials. The F.B.I. has said Mr. McCabe played no role in his wife’s campaign.
It is unclear whether Mr. Trump watched Mr. McCabe’s testimony, but one thing is certain: The president cannot fire him for it.