But a Gardner candidacy would seriously shake up the race. If he gets in, a huge question would be whether other, more tea-flavored candidates (like Buck) stay in the primary, or whether the field clears. And if Gardner does earn his party's nomination, Udall will have a very serious race on his hands. Indeed, someone as cautious as Gardner wouldn't make this leap without some very positive polling. (A PPP poll from last April had Udall up 10, but that was a long time ago in Colorado politics.)
Assuming we wind up with a Gardner vs. Udall race, that would mean, at the very least, a titanic matchup in the Rockies. It would also further stretch Democrats by forcing them to divert resources from other contests, which is exactly what the party doesn't need right now. But it's also no sure thing that Gardner would win the Republican primary, given how often we've seen establishment GOPers crash and burn. And that's certainly what Democrats would have to hope for here.
P.S. As for Gardner's House seat, it went 59-39 for Mitt Romney in 2012, so it's safely Republican.