Secret Service Director Julia Pierson has resigned after a September 19th White House security breach.  

Pierson’s resignation comes after an incident in which Omar Gonzalez, a knife-wielding Iraq War vet, allegedly managed to slip over the fence, past several layers of security, and into the White House’s East Room, where he was subdued by an off-duty agent.

Lawmakers at a congressional hearing Tuesday demanded to know how such a breach of one of the most secure buildings in the world could have taken place.

Photo by Chip Somodevilla, Getty Images

"It will never happen again,” Pierson assured lawmakers at the hearing.

Congress also questioned her about a 2011 incident in which agents failed to realize the White House had been sprayed by bullets until a housekeeper pointed out a pane of broken glass.

“You’re not taking your job seriously,” Rep. Stephen Lynch, D-Mass., said. “I have very low confidence in the Secret Service under your leadership.”

At least one lawmaker had called for Pierson’s resignation.

“I think this lady has to go,” Maryland Rep. Elijah Cummings, the most senior Democrat on the House Oversight Committee, said Wednesday. “I’m convinced that she is not the person to lead that agency.”

Administration officials had hoped Pierson, named director on March 26, 2013, could overhaul the scandal-plagued agency, which suffers from cultural problems as well as operational ones.

Not long after Pierson assumed her post, the Secret Service, still under fire from the Cartagena, Colombia, prostitution scandal the year before, was lambasted anew when it was discovered that an agent had left a bullet in a Washington hotel room after spending the evening with a woman in May 2013.

Though a Homeland Security report released the following December concluded agency leadership hadn’t “fostered an environment that tolerates inappropriate behavior,” concern that agent misconduct might endanger the first family lingered.

Then in March 2014, three counter-assault agents responsible for protecting Obama in Amsterdam were sent home after getting drunk less than 10 hours before they were expected to report for duty.

The agency has also dealt with a spate of White House fence-jumpers -- 17 in the past five years, according to Pierson -- though everyone but Gonzalez was quickly subdued on the lawn.