Nebraska ? Republican Sen. Chuck Hagel, a thorn in his own party’s side when it comes to Iraq, announced Monday that he would retire from the Senate and not seek any elected office in 2008.

“I said after I was elected in 1996 that 12 years in the Senate would probably be enough, and it is,” Hagel said.

His exit means one more seat the minority Republicans will be forced to defend, and both parties are expected to bring in heavy hitters to vie for the spot. The contenders could include Democrat Bob Kerrey, a former U.S. senator and governor, and Republican Mike Johanns, the U.S. agriculture secretary and another former governor. Republican state Attorney General Jon Bruning has already announced his plans to run.