Colorado Republican Sen. Wayne Allard said Monday he will not run for re-election in 2008 but will honor a pledge he made in 1996 to serve only two terms.
"Today, I'm announcing that I will honor my term limits pledge to the people of Colorado," he said.
The decision sets up a wide-open race. Allard's seat was once considered safe for the GOP, but Colorado voters have shown a penchant lately for replacing Republicans with Democrats.
Democrats see the race as a chance to pick up another vote in Congress after wresting two House seats and a Senate seat from Republicans the past two years. Republicans hope to stanch a long series of losses, including both houses of the state Legislature and the governor's office.
Democratic Rep. Mark Udall, a popular five-term congressman and son of former Rep. Morris Udall of Arizona, has said he was going to run for the seat whether Allard did or not. Another Democrat who has been mentioned as a potential candidate is Denver Mayor John Hickenlooper.
On the Republican side, former congressman Scott McInnis said he will run if Allard and former Gov. Bill Owens don't.
Owens, a Republican, left office last week after term limits prevented him from running again. McInnis did not immediately return calls Monday.
Another prominent Republican, anti-immigration firebrand Rep. Tom Tancredo, also has been mentioned as a possible candidate. So have Attorney General John Suthers, who said through a spokeswoman it was premature to make a decision about 2008, and John Elway, the former Denver Broncos quarterback.
Allard's political strength came into question in 2006 when Time magazine ranked him as one of the five worst U.S. senators.
Allard's chief of staff, Sean Conway, criticized the Time ranking as "more like a popularity poll" and said it was based mostly on opinion.