Secret Service Director Julia Pierson Resigns

— -- Secret Service Director Julia Pierson, who has been skewered by critics over the Sept. 19 White House security breach, has resigned, according to the U.S. Department of Homeland Security.

"Today Julia Pierson, the director of the United States Secret Service, offered her resignation, and I accepted it," Homeland Security Secretary Jeh Johnson said in a statement this afternoon. "I salute her 30 years of distinguished service to the Secret Service and the Nation."

Johnson has appointed Joseph Clancy, formerly special agent in charge of the Presidential Protective Division of the Secret Service, as the interim acting director.

"Mr. Clancy retired from the Secret Service in 2011," he added. "I appreciate his willingness to leave his position in the private sector on very short notice and return to public service for a period."

President Obama telephoned Pierson today to "express his appreciation for her service to the agency and to the country,” White House Press Secretary Josh Earnest said at today’s press briefing.

“Over the last several days, we've seen recent and accumulating reports raising questions about the performance of the agency and the president concluded that new leadership of that agency was required,” Earnest added, rejecting the notion that Obama and Johnson had bowed to mounting bipartisan pressure from Congress.

“Director Pierson offered her resignation today because she believed it was in the best interest of the agency to which she has dedicated her career," he told reporters. "The [Homeland Security] secretary agreed with that assessment. The president did as well."

As for Clancy, the interim acting director, he has “the full confidence of the president and first lady,” Earnest added, also pledging a complete review of the fence-jumping incident to be conducted by the DHS deputy secretary and reviewed by an independent panel.

Pierson’s resignation comes in the wake of 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 the congressional hearing Tuesday demanded to know how such a breach of one of the most secure buildings in the world could have taken place.

"It will never happen again,” Pierson, 55, 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 today 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 counterassault 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 – at least 16 in the past five years, according to Pierson – though everyone but Gonzalez was quickly subdued on the lawn.

ABC News’ Mike Levine, John Parkinson and Jeff Zeleny contributed to this report.