A month ago, Stuart Rothenberg made the case for why the Montana Senate seat remained a pure tossup. But now that former Gov. Brian Schweitzer is not running on the Democratic side, and Rep. Steve Daines is likely to run on the GOP side, Republicans should start this open seat race with a very narrow advantage.

First, a quick look back at Rothenberg’s description of the political landscape in Big Sky Country:

While Republicans have held the state’s lone at-large U.S. House seat since Rick Hill won it in 1996, Democrats have won 19 of the past 22 Senate races in the state, a striking record of success. Of course, that streak largely reflects the success of four longtime Democratic politicians — Mike Mansfield, Lee Metcalf, John Melcher and Baucus.

Still, the Democratic record is remarkable, especially because Republican presidential nominees have carried the state in 14 of the past 16 presidential contests. Only Lyndon B. Johnson and Bill Clinton (in 1992) carried the state — and Clinton “won” it with only 37.6 percent of the vote when independent Ross Perot divided the conservative vote.

Most of the current statewide state officers are Democrats (though not the attorney general), and the two parties have held Montana’s governorship for almost equal amounts of time since the end of World War II.

Republicans hold comfortable majorities in both houses of the state legislature, but that was not the case right before the dramatic 2010 midterm elections, when Republicans performed so well nationally in state legislative contests. Before that midterm, Republicans held a razor-thin majority in the Montana House, while Democrats held a razor-thin majority in the Montana Senate.

Democrats have time to get a quality candidate into the race but he or she will face an uphill battle. We’re moving the race from Pure Tossup to Tossup/Tilt Republican in the Rothenberg Political Report/Roll Call ratings.