HOMELAND SECURITY Secretary Jeh Johnson wasted no time Wednesday in accepting Julia Pierson’s resignation as director of the Secret Service. It had become clear, following her poor performance 24 hours earlier at a Capitol Hill hearing and the alarming revelation of a new security breach that allowed an armed felon to get close to the president, that there was no support for her leadership.

Even more important were Mr. Johnson’s recognition that the agency’s problems likely go much deeper than who is at its top and his decision to order an independent review. The string of troubling events in which White House security was breached, protocols were ignored and the president apparently was kept out of the loop demands serious attention and action. Mr. Johnson’s swift and decisive steps were reassuring.

With calls mounting from both parties for Ms. Pierson’s departure, Mr. Johnson issued a no-nonsense statement announcing her resignation. He saluted her 30 years of public service and named Joseph Clancy, formerly special agent in charge of the presidential protective division of the Secret Service, to be interim acting director. Investigation of the Sept. 19 incident in which a man was able to get into the White House will be taken over by the Department of Homeland Security, and a panel of independent experts will be convened to look at issues relating to the Secret Service.

The need for this broader look is underscored by the fact that it was only 18 months ago that Ms. Pierson was brought in as director to help remake an agency tarnished by a scandal involving agents allegedly drinking and consorting with prostitutes while on overseas trips. Ms. Pierson established new rules, but her tenure was undone by the even more serious concern that agents were not up to the job of protecting the president and his family. In addition to the Sept. 19 incident, there were revelations of a fumbled investigation of a 2011 shooting attack on the White House; the last straw was the report of an armed contractor with a criminal record who was allowed to ride in an elevator with the president during a Sept. 16 trip to Atlanta.

There is no question, as Mr. Johnson noted in his statement, that the Secret Service is comprised of men and women willing to put their lives on the line to protect others. The dedication of its staff is another reason why it is important to quickly identify and address the root problems that have come to bedevil the agency.