The outrage about the failure to stop Mr. Gonzalez escalated with news reports that law enforcement officers had previously encountered him, armed and with a map of the White House. Anger intensified after The Washington Post reported that the Secret Service had misled the public about how far Mr. Gonzalez got inside the White House. Initial reports by the Secret Service gave the impression that Mr. Gonzalez had been stopped just inside the North Portico.

But the tipping point, according to Mr. Earnest, came Tuesday night, when The Washington Examiner reported the incident in Atlanta. Law enforcement officials later confirmed that Secret Service officials were initially unaware that the private security guard riding in the elevator with Mr. Obama was armed. They discovered his weapon, they said, after he started taking pictures of the president and acting unprofessionally.

Image Ms. Pierson before testifying in the House on Tuesday. Credit... Chip Somodevilla/Getty Images

Officials said the Secret Service quickly began to investigate the incident. Hours after it occurred, on Sept. 16, senior agents met at the agency’s Atlanta field office to start an “after action review” to determine what had occurred and how it could be prevented in the future.

But the agency did not immediately inform anyone at the White House, Mr. Earnest said, and Ms. Pierson did not bring up the incident during an Oval Office meeting with Mr. Obama on Sept. 24, which had been arranged to discuss the fence-jumping case.

“I think if there’s a serious breach of the president’s security, that we would anticipate that, at a minimum, that White House officials would be informed in a timely fashion,” Mr. Earnest said.

Ms. Pierson also did not bring up the incident during several hours of testimony before the House panel on Tuesday. In an exchange with Representative Jason Chaffetz, Republican of Utah, Ms. Pierson said that she had briefed Mr. Obama about only one incident involving his safety in 2014 — the case involving Mr. Gonzalez.