Top officials responsible for security at the Capitol on Jan. 6 as it was overrun by a mob backing former president Donald Trump blamed wide-ranging intelligence failures for the deadly attack at a Senate hearing Tuesday, pointing to lapses that included a missed email warning of violence and a larger inability to recognize the threat posed by domestic right-wing extremism.

Three officials who have resigned — Capitol Police chief Steven A. Sund, House sergeant-at-arms Paul D. Irving and Senate sergeant-at-arms Michael C. Stenger — each sought to minimize their responsibility for the events on that violent and chaotic day, which resulted in the deaths of a Capitol Police officer and four others and temporarily delayed the congressional certification of President Biden’s victory.

But they each, to varying degrees, detailed how they were caught off-guard by the scale and ferocity of the pro-Trump crowd, which escalated from a relatively peaceful protest to a violent mob in a span of hours while security officials scrambled — and ultimately failed — to respond.

“None of the intelligence we received predicted what actually occurred,” Sund said at the hearing. “We properly planned for a mass demonstration with possible violence. What we got was a military-style, coordinated assault on my officers and a violent takeover of the Capitol building.”

Several efforts are underway to determine what went wrong on the day the rioters stormed the Capitol, the most serious breach of the building since British troops burned it in 1814. Federal prosecutors have filed cases against rioters, the Government Accountability Office is probing security preparations, and top congressional leaders continue to discuss creating an outside commission to investigate the attack, one modeled on the bipartisan 9/11 Commission.

But the investigations now underway by congressional committees are likely to provide the most immediate transparency. They are being conducted by the targets of the attack, lawmakers who gathered on Jan. 6 to provide final certification of the November presidential election only to find themselves under siege by pro-Trump rioters — in some cases, just seconds from potential captivity, injury or worse.

Senator after senator on Tuesday praised the heroism of the law enforcement officers who responded to the attack while at the same time pressing those in charge to account for the massive security lapse.

“We owe it to the American people to figure out how the United States Capitol, the preeminent symbol of democracy around the world, could be overtaken by an angry, violent mob,” said Sen. Amy Klobuchar (D-Minn.), chairwoman of the Senate Rules and Administration Committee.

In one key moment, Irving denied a claim made previously by Sund that Irving’s concern about “optics” drove his decision to deny a request for military assistance two days before rioters breached the Capitol.

Rather, Irving said that he, Sund and Stenger had agreed at the time that the intelligence assessment they received — indicating a pro-Trump rally similar to two others that had taken place in the weeks before — did not justify a military deployment.

“I was not concerned about appearance whatsoever — it was all about safety and security,” Irving said. “Any reference [to ‘optics’] would have been related to appropriate use of force, display of force. And, ultimately, the question on the table when we look to any security asset is, does the intelligence warrant it?”

A fourth witness, acting D.C. police chief Robert J. Contee III, whose officers engaged in some of the most violent clashes of the day, described how he was frustrated at the slow deployment of National Guard troops as the scope of the violence become clear. He recounted a phone call that included Capitol security officials, as well as D.C. leaders and Defense Department brass.

“There was not an immediate yes of, ‘The National Guard is responding,’ ‘The National Guard is on the way,’ ” he said. “The response was more asking about the plan: What was the plan for the National Guard? . . . How this looks with boots on the ground on the Capitol?”

“My response to that was simply, I was just stunned,” Contee added.

Contee and Sund both warned that the Capitol attack reflected a larger failure of domestic intelligence to take threats from homegrown extremists as seriously as those coming from foreigners. Both did so in the context of explaining their failure to act on an intelligence bulletin issued by the FBI’s Norfolk field office the day before the attack.

The report, first publicly disclosed after the attack by The Washington Post, relayed credible calls for violence: “Go there ready for war,” read one of the messages. “We get our President or we die. NOTHING else will achieve this goal.”

Sund disclosed for the first time that the bulletin was forwarded to Capitol Police through the Joint Terrorism Task Force, but it reached only as far as the department’s intelligence division. It was not forwarded to Sund or to the two sergeants-at-arms.

Contee said the D.C. police department also received the report but said it came as an undistinguished email, not as a priority alert demanding immediate attention.

“I would think that something of that nature would rise to the level of more than just an email,” he said. “I assure you that my phone is on 24 hours a day, seven days a week.”

Sund told senators that the federal intelligence community “needs to broaden its aperture on what information it collects” and called for an examination of the “view they have on some of the domestic extremists and the effect that they have.”

Sen. Gary Peters (D-Mich.), chairman of the Homeland Security and Governmental Affairs Committee, largely agreed in comments he made closing the hearing Tuesday.

“There’s no question our federal counterterrorism resources are not focused on effectively addressing the growing and deadly domestic terror threat,” he said, noting that federal agencies are eight months late in delivering a comprehensive assessment on that subject.

The two Senate committees that held Tuesday’s hearing are expected to conduct a second one next week featuring witnesses from the FBI, Pentagon and Department of Homeland Security who had a more direct role in intelligence gathering.

During the hearing, senators struggled to resolve discrepancies in the timeline of the official response to the breaching of the Capitol. One stark dispute between Sund and Irving involved their conversations on Jan. 6 as rioters entered the building. While Sund testified that the two spoke at 1:09 p.m., shortly after rioters had broken through the Capitol security perimeter, Irving said he did not speak to Sund till later.

Sund stood by his testimony, repeating several times that when he asked the sergeants-at-arms for assistance from the National Guard, he did so in the presence of his two assistant chiefs and general counsel, and that he called to check on the status of his request at 1:22 p.m. Sund’s account of the chronology that day is based on contemporaneous notes he took on Jan. 6 and his phone log, according to a person with knowledge of the records.

But Irving said he did not recall those conversations taking place, and that he was on the House floor when Sund said the call came through, monitoring the congressional joint session reviewing the electoral college results.

Video from the House chamber shows that at 1:09 p.m. Irving was on the House floor. But the camera angles shift frequently, and it was not immediately clear how long he stayed on the floor.

Irving insisted that his phone records show no contact from Sund before 1:28 p.m., when he says the then-Capitol police chief called to inform him that “conditions were deteriorating” outside and that he “might be making a request at a later time” to bring in the National Guard.

Had Sund made the 1:09 p.m. request as he claimed, Irving said, “We would have approved it immediately.” Senators asked the officials to provide phone records to resolve the dispute.

Irving also disputed speculation from Republicans loyal to Trump that House Speaker Nancy Pelosi (D-Calif.) was to blame for the security failures at the Capitol.

When asked by Sen. Josh Hawley (R-Mo.), a leader of the effort to discount the electoral college results, whether he had waited for permission from congressional leaders before deploying the National Guard, Irving said, “Absolutely not.”

He said that he “notified” and “advised” Pelosi’s office about what was transpiring and the response law enforcement officials were already mounting.

Another Republican senator, Ron Johnson of Wisconsin, suggested that the rioters were not Trump supporters, but “provocateurs” who infiltrated an otherwise peaceful crowd. Federal prosecutors have charged a variety of Trump supporters and right-wing extremists but have not identified any as having left-wing or anarchist ties.

Federal prosecutors on Tuesday revealed the latest charges in the riot, alleging that a Marine veteran who served for 20 years in the New York Police Department engaged in a vicious attack, beating a D.C. officer with a metal pole and then choking him with his own protective gear. Thomas Webster displayed “pure rage” befitting a “junkyard dog,” a federal prosecutor told a magistrate judge in White Plains, N.Y.

Key senators said they expected reforms to results from their inquest, starting with a possible restructuring of the Capitol Police Board, a four-member body that oversees congressional security matters but provides little transparency about its operations.

Sund, Irving and Stenger, who all sat on the board by virtue of their leadership positions, described a drawn-out process of meetings and negotiations as they finalized the Capitol security posture in the days leading up to the riot. Sund had to seek approval from Irvin and Stenger to call in the National Guard as the rioters breached the Capitol itself.

Sen. Roy Blunt (Mo.), the top Republican on the Rules Committee, said that structure appeared to be unworkable in an emergency, with each sergeant-at-arms focused on the security of his respective chamber.

Senators also raised the prospect that changes might be needed at the Capitol campus. Lawmakers of both parties have objected to the prospect of permanent fencing around the Capitol or more restricted access to congressional office buildings. But Klobuchar said some changes would have to be seriously considered in the wake of the attack.

“We want people to be able to visit here, but that doesn’t mean that we don’t make some smart security changes to this building,” she said. “I think people will have to realize that it’s not going to be just like it used to be.”

Rachel Weiner, Shayna Jacobs and Carol D. Leonnig contributed to this report.