U.S. officials say Tom Ridge has resigned after 23 months as the nation's first Homeland Security Secretary.
Department of Homeland Security officials say Ridge informed his senior leadership team in an e-mail Tuesday morning, and also informed the White House. A formal announcement is expected at a news conference Tuesday afternoon.
Ridge became the nation's first White House homeland security adviser a month after the 9-11 attacks. He assumed the Cabinet-level post after Congress created the Homeland Security Department, merging 22 government agencies.
He has presided over six national "orange alerts" during heightened terror concerns, but an attack never happened on his watch.