WASHINGTON

The director of the U.S. Secret Service, who faced blistering criticism for her agency’s string of breakdowns jeopardizing the security of President Obama and his family, resigned Wednesday.

Julia Pierson, 55, stepped down amid mounting pressure from Democrats and Republicans. She had led the agency for the last 16 months.

“I think this lady needs to go,” Rep. Elijah Cummings, D-Md., said Wednesday morning.

The ranking member of the House Oversight and Government Reform Committee said he had trouble sleeping Tuesday night after hearing Ms. Pierson’s testimony before the committee.

The criticism of the Secret Service came to a head after revelations that the man who breached security at the White House on Sept. 19 penetrated much farther into the building than previously disclosed.

“How on earth did it happen?” asked committee Chairman Darrell Issa, R-Calif. He stressed the fact that Omar Gonzalez, an Army veteran of the Iraq War, had breached at least five rings of security at the White House.

Mr. Gonzalez, 42, was charged with unlawfully entering a restricted building or grounds while carrying a deadly or dangerous weapon. Officials said he was carrying a knife when he jumped the White House fence, sprinted across the lawn and entered the Executive Mansion.

A prosecutor said in court last week that officers found more than 800 rounds of ammunition, two hatchets and a machete in Mr. Gonzalez’s car.

A Secret Service official who spoke on condition of anonymity said an alarm box near the front entrance of the White House had been muted when Mr. Gonzalez entered the Executive Mansion, according to The Washington Post.

Mr. Gonzalez was previously arrested in July with a sniper rifle and a map on which the Executive Mansion was marked, the prosecutor said.

The Post reported that Mr. Gonzalez ran past a sentry immediately inside the door, past the stairway leading up to the first family’s living quarters and through the East Room, before an off-duty Secret Service agent tackled him.

An initial statement from the Secret Service, approved by Ms. Pierson, claimed that Mr. Gonzalez was apprehended just inside the doors to the North Portico.

The alarm box near the entrance, designed to alert guards to an intruder, had been muted at what officers believe was the request of the usher’s office, the Post reported, citing the Secret Service official.

The officer posted inside the door appeared to be delayed in learning the intruder was about to come through, the Post reported. Officers are trained to lock the front door immediately if they learn of an intruder on the grounds.

Also revealed this week is the fact that a gun-carrying felon rode an elevator with President Obama and his protective detail — just three days before the fence-jumping incident.

That security breach occurred while the president was in Atlanta to discuss the Ebola outbreak with officials from the U.S. Centers for Disease Control and Prevention.

A private security contractor, working with the Secret Service advance team for the president’s trip, entered the elevator and began acting strangely, refusing to stop using a cellphone to record President Obama when ordered to do so.

A supervisor from the contractor’s firm fired him immediately upon learning of his behavior — and then confiscated his firearm.

Prior to the supervisor’s action, the president’s protective detail was unaware that the contractor was carrying a gun.

It was later revealed that the man had three convictions for assault and battery.

“Words aren’t strong enough for the outrage I feel for the safety of the president and his family,” said Rep. Jason Chaffetz (R-Utah), chairman of the House Oversight and Government Reform Subcommittee on National Security.

“His life was in danger. This country would be a different world today if (the contractor) had pulled out his gun.”

Testifying Tuesday, Ms. Pierson called the breakdown in White House security “unacceptable,” but called for most of the hearing to be closed to the public.

After the public hearing Tuesday, the committee held a classified hearing on the issue.

Ms. Pierson joined the Secret Service in 1984. President Obama named her the agency’s first female director last year.

After Ms. Pierson’s resignation, Joseph Clancy was appointed interim director.

Mr. Clancy was special agent in charge of the Secret Service’s Presidential Protective Division before retiring from the agency three years ago. He was one of the agents who famously jogged with President Bill Clinton.