It will be a close race, Tester is a good fit for the state and has what it takes to hold his own.
I don't see how someone who sides with Harry Reid and Barack Obama over 90% of the time on Senate votes is a good fit for a state as conservative as Montana. Perhaps he's a good fit for the Montana Democratic Party, but not for the state as a whole.
He's popular, somewhat moderate, and likeable. This should be a fun race to watch. It should also be a very close race, PPP had Rehberg up 2 vs. Tester in November.