(CNN) - A new Secret Service director is at the helm – for now. Joseph Clancy, who once headed president Obama's protective detail, has been named interim director. He replaces Julia Pierson, who was on the job just 18 months.

Her tenure cut short after a series of major security lapses – including, of course, the intruder who made it to the east room of the White House – with a knife in his pocket.

But a source tells CNN's Jake Tapper that the "final straw" came when Pierson and the agency did not tell anyone in the White House that a man with a gun managed to get onto an elevator with the president in Atlanta - three days before the White House breach.

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