by Nate Silver
When FiveThirtyEight last issued a U.S. Senate forecast — way back in July — we concluded the race for Senate control was a toss-up. That was a little ahead of the conventional wisdom at the time, which characterized the Democrats as vulnerable but more likely than not to retain the chamber.
Our new forecast goes a half-step further: We think the Republicans are now slight favorites to win at least six seats and capture the chamber. The Democrats’ position has deteriorated somewhat since last summer, with President Obama’s approval ratings down to 42 or 43 percent from an average of about 45 percent before. Furthermore, as compared with 2010 or 2012, the GOP has done a better job of recruiting credible candidates, with some exceptions.
As always, we encourage you to read this analysis with some caution. Republicans have great opportunities in a number of states, but only in West Virginia, South Dakota, Montana and Arkansas do we rate the races as clearly leaning their way. Republicans will also have to win at least two toss-up races, perhaps in Alaska, North Carolina or Michigan, or to convert states such as New Hampshire into that category. And they’ll have to avoid taking losses of their own in Georgia and Kentucky, where the fundamentals favor them but recent polls show extremely competitive races.
Since a number of you may be new to FiveThirtyEight, I’m going to go into slightly more detail than usual in explaining how we make these forecasts. You’re welcome to skip past this next section if you’re more interested in the forecasts than in how we came to them.