Are the conditions favorable enough to make Republicans odds-on favorites to gain six seats and win the Senate majority? Not quite. Six seats are a lot to gain, and Republicans are at risk of nominating subpar candidates in a number of races. But it would not take all that much to tip the balance toward them.
Our initial snapshot of the 35 Senate races follows below. For each race, I have estimated the rough probability that Democrats and Republicans will hold the seat after the 2014 election. …
Summing up the possibilities across all 35 Senate races yields a net gain of four to five seats for Republicans, just short of the six they would need to win back the majority.
However, the margin of error on the calculation is very high at this early stage. Keep in mind that in each of the last four cycles, one party (Democrats in 2006, 2008 and 2012; Republicans in 2010) won the vast majority of the competitive races. If Republicans swept all the “lean” and “tossup” races, they would gain a net of eight seats from Democrats, giving them a 53-to-47 majority in the 114th Congress. If Democrats swept instead, they would lose just one seat and would hold a 54-to-46 majority. Considering the uncertainty in the landscape, estimates from betting markets that Democrats have about a 63 percent chance of holding their majority appear to be roughly reasonable.