The F.B.I. director, Christopher A. Wray, told senators on Tuesday that he was “appalled” by the siege of the U.S. Capitol and warned that domestic terrorism is “metastasizing across the country,” while insisting that the bureau issued repeated warnings about the threat in the months before the riot.
Mr. Wray’s testimony before the Senate Judiciary Committee was his first appearance before Congress since the Jan. 6 assault on the Capitol, when a mob of Trump supporters protesting the election results stormed the building, resulting in five deaths and scores of injuries to police officers.
“That attack, that siege, was criminal behavior, plain and simple, and it was behavior that we, the F.B.I., view as domestic terrorism,” Mr. Wray said. “It’s got no place in our democracy.”
Pressed on why the F.B.I. had not been more prepared for the violence, Mr. Wray said the bureau had for months released intelligence reports related to domestic terrorism — some specifically tied to the election — both publicly and to other law enforcement agencies such as the U.S. Capitol Police.
Mr. Wray said the bureau was reviewing its actions but agreed that the insurrection was not an “acceptable result.”
“We aim to bat a thousand,” he said.
Mr. Wray said the riot was not an isolated event and that the problem of domestic terrorism had grown dramatically in recent years. He disclosed that the number of domestic terrorism investigations at the F.B.I. had doubled to 2,000 since he became its director in 2017. He emphasized that the potential for racially or ethnically motivated violence remained the greatest threat among potential domestic terrorists.
In his opening statement, Senator Dick Durbin of Illinois, the Democratic chairman of the committee, said the riot demonstrated that “for far too long, our federal government has failed to address the growing terrorist menace in our own backyard.”
He accused the Trump administration of playing down the threat from white supremacists while stoking a narrative that left-wing anarchists were the greater danger to the country.
Listing a litany of mass shootings, Mr. Durbin added: “Let’s stop pretending that the threat of Antifa is equal to the white supremacist threat.”
Mr. Wray repeatedly said in response to questions from Democratic senators that people associated with the antifascist movement known as Antifa were not involved in storming the Capitol and that rioters were genuinely Trump supporters, not posing falsely as them.
The Capitol Police has largely shouldered the blame for the Jan. 6 attack on Congress, leading to the resignation of its chief, Steven Sund, whose requests for the National Guard were denied.
Yogananda D. Pittman, the acting chief of the Capitol Police, has told Congress that there was a “strong potential for violence” but that the authorities failed to do enough to thwart the “terrorist attack.”
Indeed, there were several signs of the potential for violence on Jan. 6. Federal law enforcement officials knew that members of militias such as the Oath Keepers and far-right groups such as the Proud Boys planned to travel the Washington, some potentially with weapons. Many adherents of QAnon, a dangerous conspiracy theory that has emerged as a possible domestic terrorism threat, were also expected to attend a protest rally where Mr. Trump spoke.
In addition, the F.B.I.’s Norfolk, Va., office produced a report a day earlier warning of possible war the next day. The report mentioned people sharing a map of tunnels at the Capitol complex. However, the information was unverified and the portion that quoted “war” appeared to come from a single online thread.