There were some heated moments Tuesday when Secret Service Director Julia Pierson testified before the House Oversight and Government Reform Committee about two security breaches at the White House, one in 2011 and one less than two weeks ago. (Sarah Parnass/The Washington Post)

Just 18 months after taking the helm at the Secret Service, Director Julia Pierson spent hours Tuesday on Capitol Hill facing sharp questioning from House lawmakers incensed about a recent security breach at the White House and the misleading information the agency initially released about it.

After the hearing, top lawmakers on the House Oversight and Government Reform Committee said they would request that the Department of Homeland Security impanel a team of independent investigators to conduct a comprehensive probe of the agency.

The tense grilling followed days of revelations about security breaches that have triggered mounting criticism of the elite law enforcement agency, which is charged with protecting the president, his family and visiting foreign leaders.

Pierson sat stone-faced as several members of the House committee declared that they had lost confidence in her stewardship. Some went further, depicting the Secret Service as adrift and plagued by shortcomings after a cascade of security breakdowns that allowed a knife-wielding veteran believed to be suffering from post-traumatic stress disorder to hop the White House fence, enter through an unlocked door and dash deep into the executive mansion before being stopped.

On Tuesday evening, after the revelation of a September security lapse in an elevator in Atlanta, another committee member called for Pierson to resign. Rep. Jason Chaffetz (R-Utah) said “it’s time” for her to depart, adding that “things have gotten worse, not better, under her tenure.”

Eluding security in the White House

At the hearing, Pierson promised a full review of all tactics, including the use of force, in the wake of the Sept. 19 incident in which Army veteran Omar Gonzalez allegedly broke into the White House after the sixth breach of the compound’s fence in the past year.

“It will never happen again,” she said.

The hearing followed a report by The Washington Post that Gonzalez rushed much farther into the White House than authorities had initially disclosed.

The report, based on accounts of three people familiar with the incident, described how Gonzalez cleared the White House fence, sprinted through the unlocked front door and overpowered an officer. Gonzalez was finally tackled at the far southern end of the East Room, an 80-foot-long chamber often used for receptions or presidential addresses.

The Secret Service agent who stopped Gonzalez was off-duty but happened to be walking through the White House, according to two people familiar with the incident.

The agent had been serving on the security detail for President Obama’s daughters and had just seen the family depart via helicopter minutes earlier. He happened to be in the executive mansion when chaos broke out and the intruder dashed through the main foyer.

Pierson did not reveal during her testimony that the agent who tackled Gonzalez was not assigned to the post where he confronted the intruder, but she did share that information with committee members during a subsequent closed-door briefing, according to Rep. Gerald E. Connolly (D-Va.).

Rep. Trey Gowdy (R-S.C.) hammered Secret Service Director Julia Pierson at a House hearing on Tuesday. (AP)

The agent, who previously worked as a counterassault team member, could easily have been outside or on his way home, according to people familiar with the incident.

No officers are assigned to guard the steps to the Obama family’s private living quarters when the first family is not in the complex.

“There’s no telling how long this guy could have run around if the detail guy hadn’t happened to be there,” one person said, speaking on the condition of anonymity.

Lawmakers from both parties criticized Pierson and her agency for giving misleading and partial accounts of the security breach.

“Whistleblowers were helpful both to us and to the press. We were not getting the depth of the problem [from the information provided by the Secret Service]. We now have a better understanding,” said Rep. Darrell Issa (R-Calif.), chairman of the committee. “I think it’s very clear that the problems of the Secret Service are all fixable: human error, training, morale — these are things that can be fixed.”

Rep. Stephen F. Lynch (D-Mass.) said as he left the post-meeting briefing, “Let’s just say I’m not impressed with the way she’s handled White House security so far.”

Pierson said 16 people have come over the White House fence in the past five years, including the six in the past year. Gonzalez is the first known to have jumped the fence and made it inside the executive mansion.

“We all are outraged. . . . It is obvious that mistakes were made,” she said. “I take full responsibility. What happened is unacceptable.”

Pierson acknowledged that — until after the Sept. 19 breach — the Secret Service did not have the ability to remotely lock or unlock the front door of the White House. The bolt had to be turned by hand.

“There is no such thing as ‘business as usual’ in our line of work,” she said. “We have to be successful 100 percent of the time, and we are constantly making changes and doing everything possible to ensure that we are.”

But members of the committee were withering in their criticism.

“Have you ever heard of these guys?” asked Rep. John L. Mica (R-Fla.), holding up the blue logo of ADT, the home security company.

The bashing by lawmakers went beyond perceived failings in Pierson’s management of the agency. Lawmakers interpreted her cool, measured responses as evasive and defensive.

“I wish to God you protected the White House like you’re protecting your reputation today,” Lynch said.

Pierson replied that the Secret Service does not “take any of these incidents lightly.”

“I don’t think you’re taking it seriously,” Lynch answered.

He then added: “I’m sorry. I hate to be critical, but we have a lot at stake here. I’ve got to call it like it is. I have very low confidence in the Secret Service under your leadership.”

Pierson, who was appointed head of the Secret Service in March 2013, took over as it sought to rebound from a scandal over agents allegedly visiting prostitutes in Colombia while preparing for a presidential visit. Later, the agency faced criticism when one agent on assignment in the Netherlands was found passed out in a hotel hallway after a night of drinking.

On Sunday, The Post also described the failure of the Secret Service to recognize and promptly investigate a shooting incident in 2011 in which a gunman fired at least seven shots at the upstairs residence.

Pierson was peppered with questions about the gunfire even though it occurred before her time as director. At one point, she said one impediment to determining that shots had been fired was the fact that the attack occurred at night.

“Can you not hear at night?” yelled Rep. Trey Gowdy (R-S.C.).

Rep. Tammy Duckworth (D-Ill.) quipped that perhaps agents could have deployed flashlights.

A federal grand jury on Tuesday charged Gonzalez with one federal count of entering a restricted building or grounds while carrying a deadly or dangerous weapon. He was also charged with two violations of D.C. laws: carrying a dangerous weapon outside a home or business and unlawful possession of ammunition.

The D.C. weapons charge carries up to a five-year prison sentence, and the ammunition count up to one year in prison.

Brian Murphy contributed to this report.