Colorado Republican Senator Wayne Allard is calling it quits. Names that are currently being floated as possible replacements are former U.S. Reps. Scott McInnis and Bob Schaffer , the recently departed Governor Bill Owens, Attorney General John Suthers, and a couple of wildcards like Rep. Tom Tancredo and hall of fame quarterback John Elway.

On the Dem side, Rep. Mark Uduall has already said he will seek the seat, and Denver Mayor John Hickenlooper has been mentioned as a possible contender as well.

The Colorado seat was already widely acknowledged as probably the most vulnerable Republican seat in the country, and the NRSC wasted no time in releasing a statement saying farewell to Allard and drawing a new line in the sand for 2008:

"Republicans will retain the seat currently held by Sen. Allard and the NRSC will do everything in its power to ensure the principles of fiscal responsibility and limited effective government returns to the people of Colorado in November 2008. The voters of Colorado supported Pres. Bush over Al Gore in 2000 and again over Senator John Kerry in 2004 and Republican statewide registration is 36% compared to 30% for Democrats - ensuring Republicans a strong advantage in 2008. Retention of this seat is now a top priority for the NRSC."

JOHN ADDS: This is probably good news for GOP hopes of holding on to this seat, as Allard would have faced an uphill battle against the likely Democratic nominee Rep. Mark Udall. If former two-term Governor Bill Owens were to throw his hat in the ring, Republicans would probably be favored to hold the seat. The other prominent names mentioned on the GOP side at this early stage would likely be considered slight underdogs against Udall.

Along with the seat in Colorado, Gordon Smith in Oregon, Susan Collins in Maine, Norm Coleman in Minnesota, John Sununu in New Hampshire and Pete Domenici's seat in New Mexico (if he chooses not to run) are serious vulnerabilities for Republicans in 2008.