WASHINGTON >> Facing blistering criticism from Congress, Secret Service Director Julia Pierson acknowledged on Tuesday the agency failed in executing its plan to protect the White House when a man with a knife entered the mansion and ran through half the ground floor before being subdued.

"It’s unacceptable," Pierson told lawmakers, promising a review of how the storied but blemished agency carries out its mission of protecting the president and how it failed to intercept the intruder much earlier.

"I’ll make sure that it does not happen again," she said, declaring that she took full responsibility for the failures.

Pierson disclosed that there have been six fence-jumpers this year alone, including one just eight days before Army veteran Omar J. Gonzalez scaled the fence on Sept. 19.

Pierson appeared Tuesday before the House Oversight and Government Reform Committee.

"The fact is the system broke down," declared committee chairman Darrell Issa. "An intruder walked in the front door of the White House, and that is unacceptable."

Not only that, he said, but the intruder penetrated at least five rings of security protecting what is supposed to be one of the world’s most secure properties.

"How on earth did it happen?" he asked. "This failure … has tested the trust of the American people in the Secret Service, a trust we clearly depend on to protect the president."

Lawmakers from both parties were aghast, too, about a four-day delay in 2011 before the Secret Service realized a man had fired a high-powered rifle at the White House.

The Washington Post reported on the weekend that some Secret Service officers believed immediately that shots had been fired into the mansion but they were "largely ignored" or afraid to challenge their bosses’ conclusions that the shooting was not directed at the White House.

Such breaches, combined with recurring reports of misbehavior within the agency, cause "many people to ask whether there is a much broader problem with the Secret Service," said Rep. Elijah Cummings of Maryland, top Democrat on the committee.

Members of Congress briefed by the agency apparently weren’t told of the full extent of the breaches. Details emerged only later.

Rep. Jason Chaffetz, R-Utah, said Monday night that whistleblowers told the committee that the recent intruder ran through the White House, into the East Room and near the doors to the Green Room before being apprehended. They also reported to lawmakers that accused intruder Gonzalez made it past a guard stationed inside the White House, Chaffetz said.

On the way to the East Room, the intruder would have passed a stairwell that leads to the first family’s residence.

"I’m worried that over the last several years, security has gotten worse — not better," Chaffetz said.

Pierson said Tuesday that the front door to the White House now locks automatically in a security breach. She said that on Sept. 19 a Secret Service guard was attempting to lock one of the doors manually when the intruder knocked the agent down.

In the hours after the Sept. 19 fence-jumper incident, Secret Service spokesman Ed Donovan told The Associated Press that Gonzalez had been apprehended just inside the North Portico doors of the White House. The agency also said that night the Army veteran had been unarmed — an assertion that was revealed to be false the next day, when officials acknowledged Gonzalez had a knife with him when he was apprehended.

Senate Judiciary Committee staffers who were briefed about the investigation by the administration a week after the incident were never told how far Gonzalez made it into the building, according to a congressional official who wasn’t authorized to discuss the investigation and requested anonymity. The official said the committee later was told that the suspect had, indeed, made it far beyond the front door.

Chaffetz said the committee’s request for a briefing from the Secret Service on the incident was denied, a response he called "disappointing and frustrating."

Pierson’s predecessor, Mark J. Sullivan, apologized to lawmakers in 2012 after details emerged of a night of debauchery involving 13 Secret Service agents and officers in advance of the president’s arrival at a summit in Colombia. Sullivan retired about 10 months later.

Details of how far Gonzalez got into the White House were disclosed Monday.

Citing multiple unnamed sources, The Washington Post reported that Gonzalez ran past the guard at the front door, past the staircase leading up to the Obamas’ living quarters and into the East Room, which is about halfway across the first floor of the building. Gonzalez was eventually "tackled" by a counter-assault agent, the Post said.

Getting so far into the building would have required Gonzalez to dash through the main entrance hall, turn a corner, then run through the center hallway halfway across the first floor of the building, which spans 168 feet in total, according to the White House Historical Association.

Since the incident, the White House has treaded carefully. Although White House spokesman Josh Earnest acknowledged the president was "obviously concerned" about the intrusion, he expressed confidence in the Secret Service as recently as Monday.

It would be untenable for any president, not just Obama, to pointedly criticize the men and women who put themselves at risk to protect his life and family. That inherent conflict of interest means Congress, not the executive branch, is the most effective oversight authority for the Secret Service, its agents and officers.

"The president and the first lady, like all parents, are concerned about the safety of their children, but the president and first lady also have confidence in the men and women of the Secret Service to do a very important job," Earnest said.