If I were Juneau, I'd wait until the seat opens up in 2018 when Zinke tries to take down Tester. Tester's campaign would bolster her numbers substantially, and I think she could win an open seat.
Midterms.. They are almost invariably bad for Democrats now, as their base becomes more and more minority-oriented....
Democrats can hold red state seats in midterms (sometimes, but picking one up, especially a statewide one, would be very difficult. Zinke is also a strong candidate, although I don't know much about the bench.
Democrats need Montana to be competitive at every office. Small states are too often overlooked. Glad they're fielding a relevant candidate.
Montana is not a small state.