5 Factors That Will Decide Control of the Senate

As we hit a lull in the presidential campaign, a look at several important Senate races.

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The presidential race is settling into its summer doldrums. The nominating contests are over and the two sides are relentlessly pounding each other over the airwaves, while speculation runs rampant over who Mitt Romney will tap as his vice presidential nominee.

So it's a good time to check out the main undercard: the battle for control of the Senate. Coming into the cycle, Republicans were crowing about the 23 seats Democrats had to defend as compared with the 10 seats the GOP had to worry about. It wasn't a question of whether the GOP would retake the Senate but by how much. But Maine GOP Sen. Olympia Snowe's February blindside announcement that she was retiring was the anchor of a political reset that has made the fate of the Senate anyone's guess. Republicans need to pick up three seats, or four if Vice President Joe Biden is still presiding as president of the Senate after next January 20. Even with former Sen. Bob Kerrey trying to reclaim his Nebraska seat (vacant with Democratic Sen. Ben Nelson retiring), it seems a foregone conclusion that Republicans will pick it up. Beyond that, things get interesting. Here are five story lines to follow in the battle for Senate control.

[See a collection of political cartoons on the 2012 campaign.]

Opportunities lost. One race that wasn't supposed to be on the radar is the contest to replace Indiana Sen. Richard Lugar, who lost his primary to movement conservative favorite Richard Mourdock. Lugar would have been a slam-dunk to hold the seat, so the Tea Party has once again jeopardized a safe GOP win—shades of Delaware, Colorado, and Nevada in 2010. Two others to watch are the races unfolding in Wisconsin and Florida. The Badger State will be the site of another Tea Party versus establishment showdown. Movement conservatives are gunning for establishmentarian icon Tommy Thompson, who is favored in the August 14 primary. "There are a lot of Republicans in Wisconsin who don't think he's conservative enough," says Kyle Kondik, a political analyst at the University of Virginia's Center for Politics. In the Sunshine State, Sen. Bill Nelson is vulnerable but Rep. Connie Mack IV, the GOP front-runner to take him on, has been dogged by a history of financial difficulties and violent altercations. "National Republicans have not been very impressed with him so far," says Jessica Taylor, a senior analyst at the Rothenberg Political Report. "It's not looking, at least to them right now, that it's going to be competitive." The Michigan race, where Sen. Debbie Stabenow is seen as weak, also hasn't shaped up as being as competitive as expected.

Personality tests. Then there are races that are more competitive than they should be. Montana Democrat Jon Tester and Massachusetts Republican Scott Brown are about as opposite as can be, but, says Taylor, "in both those cases, you're seeing a personality making the race interesting." Both represent states that typically strongly support the other party—making them top targets—but each exhibits a profile and political independence that resonate with voters. As a result, they both stand a chance of weathering tough races.

[See a collection of political cartoons on Congress.]

Right candidate, wrong year? When Democratic Sen. Kent Conrad of North Dakota announced his retirement in early 2011, many observers assumed the red state seat would slide easily into the GOP column. Wrong. Former state Attorney General Heidi Heitkamp, a Democrat, has run a strong enough race to keep the contest in the toss-up category. But North Dakotans are going to cast their ballots for Romney by a wide margin. "How much better is Heidi Heitkamp going to have to do than Obama to win?" the Cook Political Report's Jennifer Duffy asks. "Ten points? Twelve points?" At the same time, former Hawaii Gov. Linda Lingle "could be one of the Republicans' best recruits in the country, but it could be one of the worst states in the country," says Taylor. After all, Hawaii is President Obama's birth state, so he's going to clean up there. Nevertheless, Lingle has kept the race competitive. She's even launched her own 24-hour cable channel on the islands. Seriously.