If Republicans win six of the seven and don't cede any of their own seats -- two of which appear on our top 11 races -- they will reclaim the majority. If they win five of seven, they will have to peel off another pickup, assuming again that they don't cough up seats to Democrats, which is not a lock.
It's been a roller coaster political year, with the government shutdown doing immense damage to the GOP brand and the troubled rollout of Obamacare setting back Democrats in a big way. For now, Obamacare remains a major albatross for congressional Democrats.
The big question is this: What will be the dominant political theme this time next year? The answer to that question could well determine which party controls the Senate beginning in 2015.
Below is our latest rundown of the top 10 races most likely to change party control. As always, No. 1 is the seat most likely to flip.
To the Line!
10. Georgia (Republican-controlled) and Michigan (Democratic-controlled). A nasty and chaotic GOP primary in Georgia is Democrat Michelle Nunn's best friend. So far, she's been getting one. Rep. Paul Broun assailed fellow Republican Rep. Jack Kingston's comments about fixing Obamacare, illustrating the danger in GOP circles of being perceived as soft on the issue. Meanwhile, Rep. Phil Gingrey (R) has already parted ways with his top campaign strategists -- never a good sign. In Michigan, Obamacare's issues are clearly a concern for Rep. Gary Peters (D), who was one of more than three dozen Democrats who bucked the party to vote for a GOP fix. (Previous rankings: 10)
9. Iowa (D): A poll from GOP automated pollster Harper Polling late last month showed Rep. Bruce Braley (D) leading his lesser-known potential GOP opponents. He led former U.S. attorney Matt Whitaker 41 percent to 37.5 percent, energy executive Mark Jacobs by five points and state Sen. Jodi Ernst by six points. Braley has to be considered the favorite, especially with a clear primary, but this is a swing state, and a solid Republican and/or a good year makes this a very winnable race for the GOP. (Previous ranking: 9)
8. Kentucky (R): Senate Minority Leader Mitch McConnell (R) recently got a boost when the U.S. Chamber of Commerce launched an ad buy on his behalf. The ads were the latest evidence that this is one of the purest establishment vs. tea party contests you’ll see. What’s most interesting about this one is that McConnell – apart from his status as Senate GOP leader -- is openly bad-mouthing groups like the Senate Conservatives Fund, which is backing opponent Matt Bevin. The stakes here are huge. The Democratic candidate is likely to be Kentucky Secretary of State Alison Lundergan Grimes. (Previous ranking: 7)
7. North Carolina (D): The Tar Heel State moves up the line after what's been a tough month for Sen. Kay Hagan (D). Even Democratic polling shows her image has taken a hit amid the backdrop of Obamacare's troubled rollout. She got reinforcements this week in the form of a Senate Majority PAC ad buy, but Hagan's outlook isn't what it was a couple of months ago when all the news in this race centered on Republican Thom Tillis's unsteady campaign rollout. Hagan can court a liberal base of young and minority voters tapped by the Obama campaign twice that other Democrats on this list don't have. Still, she'll have her work cut out for her if the political climate stays as it is. (Previous ranking: 8)
6. Louisiana (D): Sen. Mary Landrieu (D) said in an interview this week that she would vote for Obamacare all over again. You could basically hear the GOP celebrating that quote, which is sure to be featured in an attack ad or two come next year. Rep. Bill Cassidy remains the clear GOP front-runner, but the Senate Conservatives Fund is backing his opponent, Rob Maness. (Previous ranking: 6)
5. Alaska (D): Roll Call’s Kyle Trygstad made a very interesting point last week: there will be two Dan Sullivans running for statewide office in Alaska next year. One is the Anchorage mayor running for lieutenant governor; the other is the former state Natural Resources Commissioner running for Senate. Both are expected to be formidable candidates, and the thought is that their advertising could benefit one another. The latter Dan Sullivan faces Lt. Gov. Mead Treadwell and 2010 nominee Joe Miller in the primary to face Sen. Mark Begich (D). (Previous ranking: 5)
4. Arkansas (D): Sen. Mark Pryor invoked the Bible in an ad this week, a decision with potential to resonate with voters in this deeply religious state. Like all incumbents in red states, Pryor is desperate to change the subject from Obamacare's troubled rollout. But Republicans will do all they can to prevent him from doing so. Rep. Tom Cotton is the likely GOP nominee. (Previous ranking: 4)
3. Montana (D): A recent poll from Democratic automated pollster Public Policy Polling showed Rep. Steve Daines (R) starts this race as a clear favorite, leading Lt. Gov. John Walsh (D) by 17 points and former lieutenant governor John Bohlinger (D) by 15. The Democratic establishment is behind Walsh, and it remains to be seen how formidable Bohlinger will be. The man Bohlinger served with, former governor Brian Schweitzer (D), says he will be staying neutral. (Previous ranking: 3)
2. West Virginia (D): This race has been pretty quiet so far. The balance of the contest looks largely as it has for months: Rep. Shelley Moore Capito (R) is the clear favorite in this open race. The national Democratic brand is toxic here, which means Secretary of State Natalie Tennant (D) will have to take a page out of the Manchin-Tomblin playbook and keep the Obama administration at a very safe distance to even have a chance. (Previous ranking: 2)
1. South Dakota (D): A recent PPP poll showed this race tightening, with heavy front-runner and former Republican governor Mike Rounds's lead shrinking to six points over Democrat Rick Weiland. Still, don't hold your breath for a Weiland upset; national Democrats don't even seem completely sold on his candidacy. (Previous ranking: 1)