1. Montana (Open D, Sen. John Walsh retiring) (Previous ranking: 3)
Montana Democrats are on their third candidate of the cycle at this point (fourth, if you count Brian Schweitzer's planned-then-canceled bid) after Walsh withdrew following graduate-school plagiarism revelations. That, in a nutshell, shows why the state has been the Democrats worst Senate race of 2014. It's almost hard to remember that last year, most analysts believed either Sen. Max Baucus or the former Gov. Schweitzer would hold the seat for their party. Now, GOP Rep. Steve Daines is nearly certain to win against Democratic state Rep. Amanda Curtis, which will mark the first time a Republican will hold the seat in more than 100 years.
2. West Virginia (Open D, Sen. Jay Rockefeller retiring) (Previous: 2)
Democratic Secretary of State Natalie Tennant hasn't done badly at all in this race, but GOP Rep. Shelley Moore Capito is just too strong and the state too conservative. This race has never really been on the radar, despite some late July spending by Senate Majority PAC—which just happened, coincidentally we're sure, to almost match the $250,000 Rockefeller donated to the Democratic super PAC this year.
3. South Dakota (Open D, Sen. Tim Johnson retiring) (Previous: 1)
Almost overnight, this race has risen from the dead. Make no mistake: Former GOP Gov. Mike Rounds is still the favorite here. But a coalition of outside groups has been hammering Rounds on his involvement in a visa scandal, and the Democratic Senatorial Campaign Committee said its internal polls showed a close-enough race to prompt a late $1 million TV blitz that started this week. The National Republican Senatorial Committee is responding with $1 million of its own. But with Rounds, Democrat Rick Weiland, and former Sen. Larry Pressler—a former Republican-turned-Obama-praising independent—splitting votes, each side faces a puzzling question of where to direct its firepower. While Rounds still solidly holds control of this race, Republicans are lamenting a lack of effort from what should have been a sure-thing campaign, forcing them to spend money in an unexpected place while other races around the country remain tightly contested.
4. Louisiana (D, Sen. Mary Landrieu) (Previous: 4)
The last few months have dulled some of the shine on Landrieu's vaunted political operation. First were a series of damaging stories about billing taxpayers for private plane rides, followed by news that her campaign manager was being replaced just a month before Election Day. Both have increased the palpable sense that the Bayou State's three-term senator is an underdog in her fight against GOP Rep. Bill Cassidy. Polls show the Republican physician, whose own campaign hasn't blown anyone away, with a slight edge on Landrieu. Still, this race is headed to a Dec. 6 runoff, and it's impossible to predict what that one-month contest will look like. (For example, whether the Senate majority is still at stake would have a major effect on the campaign.)