Republicans have lost their top potential recruit in Colorado, with Rep. Cory Gardner (R) opting not to challenge Sen. Mark Udall (D) in 2014.

"I've got work to do, I'm not in a hurry to run for another office," Gardner told the Denver Post. "I think the most important thing for people is to know now. I needed to make a decision now, and I'm fully committed to make sure the GOP nominee will win in 2014."

Gardner, 38, wasn't expected to challenge Udall, but he is considered the GOP's next big thing in the Rocky Mountain State.

Udall isn't a top GOP target either. Despite coming from a swing state, he's got good personal approval ratings, and the GOP bench in Colorado remains thin.

Gardner is expected to take a look at challenging Sen. Michael Bennet (D-Colo.), who is considered more vulnerable, in 2016.

Several Republicans recently announced challenges to Gov. John Hickenlooper (D) in 2014 -- including former congressman Tom Tancredo and Secretary of State Scott Gessler -- but so far non have jumped into the race against Udall.