Updated from 8:25 a.m. EST

Andrew Card, the career government operative who devised political strategy for the last three Republican administrations, resigned Tuesday as President Bush's chief of staff.

Card was replaced by White House budget director Josh Bolten. President Bush announced the moves in a morning press conference.

"Earlier this month, Andy raised the possibility of his resignation," Bush said. "He said it might be time to return to private life. This past weekend, I accepted Andy's resignation."

Since November 2000, Card has been chief of staff to Bush. He was the secretary of transportation for two years under the previous President Bush and served as that administration's deputy chief of staff. Under President Reagan, Card was special assistant to the president for intergovernmental affairs.

The 58-year-old Massachusetts native is perhaps best know to the public as the man who alerted Bush to the terrorist attacks on Sept. 11, 2001. Card whispered into the president's ear during a meeting with elementary school students in Sarasota, Fla.

The surprise resignation comes six months ahead of key midterm elections where Republicans are in danger of losing seats in both houses of Congress. The president's approval rating continues to slip, hurt by the halting response to Hurricane Katrina and problems with a Supreme Court nominee in October.

"It is a different season, and Josh Bolten is the right person for that season," Card said Tuesday.