A California man who the authorities say ran through a security perimeter and fired a gun outside a packed black-tie gala in Washington on Saturday was charged on Monday with trying to assassinate President Trump.

Prosecutors said the man, Cole Tomas Allen, 31, of Torrance, Calif., came to the nation’s capitol with the intention of carrying out a political assassination. He brought a pump-action shotgun, a .38-caliber handgun and three knives, officials said.

Mr. Allen appeared briefly in federal court in Washington on Monday, wearing a neon blue jumpsuit. He did not enter a plea and is likely to remain behind bars indefinitely. A magistrate judge scheduled a detention hearing in the case for Thursday.

Mr. Allen’s sudden sprint past a security checkpoint while carrying deadly weapons created a harrowing security incident for the more than 2,000 people attending the White House Correspondents’ Association dinner at the Washington Hilton. The episode renewed questions about political violence and the security measures necessary to protect a president who has been the target of multiple assassination attempts.

In a federal affidavit unsealed on Monday, an F.B.I. agent said that around 8:40 p.m. on Saturday, Mr. Allen approached a security checkpoint inside the hotel, where Mr. Trump, Vice President JD Vance and members of the cabinet were attending the dinner in the ballroom one floor below.

Mr. Allen ran through a magnetometer holding a 12-gauge pump-action shotgun, and Secret Service agents “heard a loud gunshot,” the affidavit stated. One agent was shot in the chest but was wearing a bulletproof vest, according to the affidavit, which did not say that it was Mr. Allen who shot the agent.

At a news conference after Mr. Allen’s court appearance, the acting attorney general, Todd Blanche, said the injured agent drew his gun and fired five times at Mr. Allen, who fell to the ground and was arrested. Mr. Allen was not shot and had only minor injuries, the affidavit said. In addition to the shotgun, Mr. Allen was also in possession of a .38-caliber pistol when he was arrested.

Mr. Blanche said investigators believed the suspect fired his weapon because a spent shotgun shell was found inside its chamber, but he noted that more forensic examination would be done to determine exactly what happened.

The sound of gunfire outside the hotel ballroom led to a security lockdown, as guests in tuxedos and cocktail dresses crouched under their tables. Mr. Trump and members of his administration were rushed out of the ballroom, unharmed.

Shortly before the attack, Mr. Allen sent an email to his family and a former employer in which he expressed deep anger at the administration and the president, the affidavit said. Administration officials were the suspect’s “targets, prioritized from highest-ranking to lowest,” according to a copy of the roughly 1,000-word document shared by two law enforcement officials who were not authorized to disclose the information.

Mr. Allen also expressed surprise that he was able to check into the hotel a day before the event with a shotgun, a handgun and a knife, according to the document, parts of which were cited in the F.B.I. affidavit.

The attack has raised fresh questions about whether the Secret Service is adequately prepared to protect the president in an age of rising threats and political violence. Officials insisted that security measures at the dinner worked as intended, noting that Mr. Allen never made it into the ballroom.

“I want to make this clear: This man was a floor above the ballroom with hundreds of federal agents between him and the president of the United States,” Mr. Blanche said at the news conference.

While officials have said the evidence indicates the gunman acted alone, Mr. Blanche also said on Monday that investigators were working to determine if he had any connections to left-wing activists. They are also interviewing his relatives and friends, and combing through his online activity to better understand his motives.

Speaking to reporters at the White House earlier on Monday, Karoline Leavitt, the White House press secretary, said that Mr. Trump had confidence in the Secret Service, and she praised the “heroic” agent who “took a bullet to the chest” on Saturday night. “Thankfully, he was saved by his bulletproof vest,” Ms. Leavitt said.

Still, she said, Susie Wiles, the White House chief of staff, plans to meet this week with officials from the Secret Service, the Department of Homeland Security and other agencies to review security practices for presidential events in the coming months.

Ms. Leavitt sought to blame the attack on Democrats and some members of the news media. She accused them of a “systemic demonization” of Mr. Trump that “helped to legitimize this violence and bring us to this dark moment.” She called it a “left-wing cult of hatred against the president and all of those who support him and work for him.”

On Sunday night, Mr. Trump told “60 Minutes” that he told agents during the shooting to “wait a minute” as they urged him to get down, saying he was curious to see what was happening. He said he finally dropped to the floor with the first lady, Melania Trump. “My thought was, ‘I’ve been through this a couple of times before,’” but she had not, he said.

This was the third attempted assassination of Mr. Trump in less than two years, Ms. Leavitt noted. On July 13, 2024, a bullet nicked Mr. Trump’s ear while he was delivering a campaign speech in Butler, Pa. The 20-year-old gunman, Thomas Crooks, fired several shots at Mr. Trump before the Secret Service returned fire and killed him.

On Sept. 15, 2024, a man armed with a rifle hid in the shrubbery at the Trump International Golf Club in West Palm Beach, Fla., plotting to shoot Mr. Trump. The man, Ryan W. Routh, who never opened fire, was convicted of attempted assassination and sentenced to life in prison.

Just two months ago, a man carrying a shotgun approached the gates of the president’s Mar-a-Lago home in Florida. The man, who had traveled there from North Carolina, was shot and killed.