If Democrats lose the Senate this fall, it will be in part because of the inhospitable map they face: The party is defending seven seats in states Mitt Romney won in 2012, including four incumbents. But the map looks almost equally fraught for Republicans in 2016, which party operatives readily acknowledge: The GOP must defend 24 seats, compared with just 10 for Democrats. GOP incumbents are up in five states that President Obama won twice—Florida, Iowa, Ohio, Pennsylvania, and Wisconsin—and two states Obama won once, North Carolina and Indiana.
Plus, the potential for GOP intra-party fights—Sen. Lisa Murkowski of Alaska, who lost a primary bid in 2010, could very well get a serious challenge again—and possible big retirements, like Sen. John McCain of Arizona, could put additional seats into play.
For Democrats, by contrast, Senate Majority Leader Harry Reid and Sen. Michael Bennet of Colorado are the only two incumbents who thus far look likely to have competitive races.
According to the The Cook Political Report's ratings for 2014, there are plenty of potential places where Republicans could pick up extra seats this fall: Seven Democratic-held seats are currently toss-ups, and three—Montana, South Dakota, and West Virginia—are expected Republican pickups.
A big win by the GOP would require the party to pick up most of the deep-red states with Democratic incumbents, like Alaska and Louisiana, as well as purple states that lean Democratic in presidential years. Topping that list are Colorado, Iowa, North Carolina, and even New Hampshire, perennial presidential swing states that are home to competitive races this cycle and will host Senate races next cycle as well.
Nick Ryan, an Iowa-based strategist and president of the American Future Fund, named Iowa, Colorado and New Hampshire as "stretch" states the GOP needs to win this fall in order to help pad the margins and prove that it can win outside of red states in 2016.
"Those stretch states are vital in 2014—because if you do buy into the analysis that the environment's right and you have a president that's not very popular, you have to be able to pick up some seats like this," he said. For example: "A Scott Brown victory in New Hampshire makes it possible that you could actually defend a Republican majority in 2016."
The GOP's challenge in 2016 is twofold: The party has more territory to defend, first of all, and it will have to do so with a presidential-year electorate that leans far more Democratic. The class of GOP senators up in 2016 were elected in the GOP wave of 2010—and especially in blue states, they will face a substantively different group of voters than the one that first elected them.
Perhaps at the top of that list are Pennsylvania's Pat Toomey and Wisconsin's Ron Johnson, both of whom are expected to face tough reelection races in 2016.