Jon Tester (D-inc): 42
Mark Racicot (R): 49
It's a bit of a mixed bag for Jon Tester. He's leading his announced opponents -- '08 Lt. Gov. nominee Steve Daines and "crisis management" CEO Neil Livingstone -- by double-digit spreads, and his job approval rating is 50/40, a spread so healthy that PPP is calling him one of the most popular Senators in the country. However, if current Rep. Denny Rehberg took the plunge, Tester would be in for a real challenge. (And an even bigger challenge if John Cornyn somehow managed to lure ex-Gov. Mark Racicot into the race, but that seems unlikely.)
Rehberg has until March 2012 to decide on the race, which buys him plenty of time to assess the situation -- and given the B-grade level of Livingstone and Baines, he'd have a good shot at clearing the field, too, unless one or both of them decides to run as an out-and-proud insurgent teabagger.