The battle for control of the Senate hasn't slowed down since we last looked in on the most competitive races of the cycle. In recent weeks, Democrats landed big recruits in Kentucky and Georgia, while Republicans got the man they wanted in Arkansas.
Republicans are expected to have to pick up six seats in 2014 to win back the majority. Open races in West Virginia, South Dakota and Montana present golden opportunities to make gains, while vulnerable Democratic incumbents in Arkansas, Alaska, Louisiana and North Carolina represent four more pickup opportunities.
And now, to the Line! Our list of the 10 Senate seats most likely to change control in 2014 is below. As always, No. 1 is most likely to flip.
10. Georgia (Republican-controlled): Michelle Nunn announced her candidacy last month, effectively putting this one on the table for Democrats. She’s got a great name for this state (where her father, Sam Nunn, is a former senator), but this is her first political campaign. On the GOP side, the new entrant is David Perdue, cousin of former Georgia governor Sonny Perdue (R), who becomes the fifth major GOP candidate in a field that could break any which way. Who emerges from that primary will be a huge determining factor when it comes to whether this race is competitive. (Previous ranking: 10)
9. Iowa (Democratic-controlled): Democrats are happy with what they've seen so far from Rep. Bruce Braley (D), a capable fundraiser who looks set to cruise to his party's nomination without any trouble. The Republican primary, meanwhile, lacks a clear front-runner. It features a former Senate aide, a conservative radio host, a former U.S. attorney, a state senator and possibly a retired businessman, too. Gov. Terry Branstad (R) says he likely won't endorse in the primary, but he had an awful lot of nice things to say about state Sen. Joni Ernst (R) last week, so keep an eye on her candidacy. Democrats have the advantage in this open race right now, but the political contours of the state suggest it's not out of the question that Republicans can compete there. (Previous ranking: 8)
8. North Carolina (D): It's been a rough couple of months for state House Speaker Thom Tillis (R), who has been plagued by headlines about major donors getting seats on the UNC Board of Governors and the money he's received from the gaming industry, and criticism over his decision to launch a Senate campaign while the legislature was still in session. None of it means Tillis can't compete with Sen. Kay Hagan (D), who remains vulnerable. But his rough start was not the way to begin what promises to be a hard-fought campaign. (Previous ranking: 6)
7. Kentucky (R): The last month or so hasn't been very good to Senate Minority Leader Mitch McConnell (R). He not only drew what he had most hoped to avoid — a self-funding primary challenge running to his ideological right — but also a credible Democratic challenger in Secretary of State Alison Lundergan Grimes. Grimes is green — as evidenced by her disastrously bad first announcement of her Senate candidacy — but the Democratic Senatorial Campaign Committee will ensure she has a solid team around her to make sure she avoids further rookie mistakes. Polling suggests it's already a close race. We think McConnell still is a slight favorite to come back to the Senate in 2015, but his chances got longer over the past month. (Previous ranking: 9)
6. Alaska (D): This is another state with a crowded and unwieldy GOP primary that will say plenty about how well Republicans compete in November. Lt. Gov. Mead Treadwell appears to be the favorite, and 2010 nominee Joe Miller is the guy Republicans definitely don’t want. In the middle is the potential wild card, state Natural Resources Commissioner Dan Sullivan -- not to be confused with the Anchorage mayor of the same name -- who recently deployed to Afghanistan. Treadwell didn’t get off to a fast start, raising just $180,000 in the first six months of the year, and there is speculation that Sullivan, who is not a candidate yet, could start looking more attractive as an alternative. (Previous ranking: 4)
5. Louisiana (D): Rep. Bill Cassidy (R) had a strong fundraising quarter, hauling in over $1 million for his bid against Sen. Mary Landrieu (D). His only Republican opponent, meanwhile, brought in just $40,000, more good news for the GOP front-runner. Landrieu has shown ability to win in competitive races, but 2014 promises to be her toughest test yet. (Previous ranking: 5)
4. Arkansas (D): Rep. Tom Cotton (R) is the rare GOP recruit with the ability to unite the conservative grass roots and the GOP establishment. And that spells trouble for Sen. Mark Pryor (D), the Senate's most vulnerable incumbent. Pryor has already taken criticism over the airwaves from both conservative groups on his right and a leading gun-control organization on his left. When Cotton committed to running, things looked even bleaker for the Democrat. (Previous ranking: 3)
3. Montana (D): Former governor Brian Schweitzer’s (D) surprise decision not to run effectively turned a seat that leaned Democratic into a seat that leans Republican. And since his announcement, a trio of big-name potential female Democratic candidates have passed on the race: state Auditor Monica Lindeen, Emily’s List President Stephanie Schriock, and state schools superintendent Denise Juneau. On the GOP side, we’re still waiting to see if freshman Rep. Steve Daines jumps in. For now, former state senator Corey Stapleton is the front-runner. (Previous ranking: 7)
2. South Dakota (D): Four Democratic senators from the Dakotas have lined up behind Rick Weiland as the Democratic standard-bearer in this race, but national Democrats are still in search of an alternative, not believing Weiland can make a race of it against likely GOP nominee and former governor Mike Rounds. Democrats' best hope here may be the possibility that Rounds gets a legitimate primary challenger who can damage his candidacy or somehow upset him. For now, there’s no evidence that will happen. (Previous ranking: 1)
1. West Virginia (D): Not even Rep. Shelley Moore Capito (R) could have dared to imagine that the path to the Senate would have opened up so well for her back in late 2012 when she announced her candidacy. Democrats have watched candidate after candidate say "no" to the race. The latest candidate to take a pass is West Virginia Supreme Court Justice Robin Davis. All Democratic hope now lies in Natalie Tennant, the secretary of state and, more interestingly to us, the former West Virginia University mascot. (Previous ranking: 2)
-- Chris Cillizza contributed to this post