From Larry J. Sabato’s Politico post, “Can Democrats Retake the Senate in 2016?“:
It’s still too early to predict the Senate’s makeup in 2016, but it’s not too early to start thinking about who could land on the list of endangered senators. And in the 2016 cycle, it’s more likely to be a Republican than a Democrat.
…Republicans must defend seven incumbents that represent states carried by President Obama in 2008 and 2012: Kelly Ayotte of New Hampshire, Chuck Grassley of Iowa, Ron Johnson of Wisconsin, Mark Kirk of Illinois, Rob Portman of Ohio, Marco Rubio of Florida, and Pat Toomey of Pennsylvania. An eighth state Obama carried in 2008 but narrowly lost in 2012–North Carolina, home to two-term Republican Richard Burr–also merits mention with these other states.
…under the right conditions–i.e., strong Democratic Senate candidates combined with a solid national lead for the Democratic presidential nominee–all seven of the other seats are vulnerable. Three of the states (Illinois, Pennsylvania, and Wisconsin) are more Democratic than the nation as a whole and have a history of voting Democratic for president even when the party loses a close race nationally, as in 2000 and 2004. This reality has placed Kirk, Toomey and Johnson at the top of the endangered senators list.
In recent presidential cycles, there has been a consistent uptick in the correlation between Senate and presidential election outcomes. That is to say, the Senate result in a state has tended to be increasingly aligned with the state’s presidential result. Excluding Maine and Vermont (where independents Angus King and Bernie Sanders won, respectively), the correlation in 2012 between Senate and presidential results was a strong .78 (1.0 would be strongest). This was the third straight cycle to see an increase in this correlation, and it is the highest since 1956…
Sabato adds, “More and more, voters are inclined to cast straight-ticket ballots when they enter the voting booth.” He explains that “the most competitive races–the three toss-ups and the six leaners (two Democratic seats and four Republican ones) also take place in what should be among the most competitive presidential states.”
“This,” Sabato concludes, “is a recipe for Senate elections that are mainly tied to the presidential results.” It’s early yet, but, given Sabato’s impressive track record in political predictions, Dems should allocate resources with his insights in mind.