In announcing his retirement, Mr. Hagel will fulfill a promise made when he first ran for the Senate in 1996 that he would serve only two terms.

From The New York Times:

Senator Chuck Hagel, the Nebraska Republican and outspoken critic of the Iraq war who had been mulling a run for president, will retire at the end of his term in early 2009 and will not run for the White House, aides said on Saturday.

In announcing his retirement, Mr. Hagel will fulfill a promise he made to voters when he first ran for the Senate in 1996 that he would serve only two terms. But his decision presents yet another challenge for the Republican Party in its effort to stop Democrats from extending their majority in Congress next year.

Former Senator Bob Kerrey, a Nebraska Democrat who has been president of the New School university in New York City since leaving office in 2001, has said that he might return to Nebraska to run for office again. Mr. Kerrey is also a former governor of Nebraska.