NATE SILVER,FIVE THIRTY EIGHT
If Americans elected an entirely new set of senators every two years — as they elect members of the House of Representatives — this November’s Senate contest would look like a stalemate. President Obama remains unpopular; his approval ratings have ticked down a point or two over the past few months. But the Republican Party remains a poor alternative in the eyes of many voters, which means it may not be able to exploit Obama’s unpopularity as much as it otherwise might. Republicans usually have a turnout advantage, especially in midterm years, and their voters appear to be more enthusiastic about this November’s elections. Still, the gap is not as wide as it was in 2010.
The problem for Democrats is that this year’s Senate races aren’t being fought in neutral territory. Instead, the Class II senators on the ballot this year come from states that gave Obama an average of just 46 percent of the vote in 2012.1
Democrats hold the majority of Class II seats now, but that’s because they were last contested in 2008, one of the best Democratic years of the past half-century. That year, Democrats won the popular vote for the U.S. House by almost 11 percentage points. Imagine if 2008 had been a neutral partisan environment instead. We can approximate this by applying a uniform swing of 11 percentage points toward Republicans in each Senate race. In that case, Democrats would have lost the races in Alaska, Colorado, Louisiana, Minnesota, New Hampshire, North Carolina and Oregon — and Republicans would already hold a 52-48 majority in the Senate.
It therefore shouldn’t be surprising that we continue to see Republicans as slightly more likely than not to win a net of six seats this November and control of the Senate. A lot of it is simply reversion to the mean.2 This may not be a “wave” election as 2010 was, but Republicans don’t need a wave to take over the Senate.
However, I also want to advance a cautionary note. It’s still early, and we should not rule out the possibility that one party could win most or all of the competitive races.
It can be tempting, if you cover politics for a living, to check your calendar, see that it’s already August, and conclude that if there were a wave election coming we would have seen more signs of it by now. But political time is nonlinear and a lot of waves are late-breaking, especially in midterm years. Most forecasts issued at this point in the cycle would have considerably underestimated Republican gains in the House in 1994 or 2010, for instance, or Democratic gains in the Senate in 2006. (These late shifts don’t always work to the benefit of the minority party; in 2012, the Democrats’ standing in Senate races improved considerably after Labor Day.) A late swing toward Republicans this year could result in their winning as many as 10 or 11 Senate seats. Democrats, alternatively, could limit the damage to as few as one or two races. These remain plausible scenarios — not “Black Swan” cases.