True, but LA had never popularly elected a Republican to either of its seats in the Senate, and when Breaux retited in 2004 Vitter won quite comfortably.
My point is that, while we can’t take anything for granted in MT, it’s not as if it’s freaking Hawaii or Maryland. It gave Romney a big victory margin in 2012, and has a long history of electing Republicans in statewide federal elections over the past 25 years (except for Baucus, and Tester in 2006 and 2012).
Senate races in MT have frequently been a problem for the GOP going back a century. They’ve only won in 1946 (Zales Ecton) & 1988, 1994 and 2000 (Conrad Burns). The GOP has lost by the narrowest of margins in many of the races.