Senate Republicans will be playing a lot of defence in 2016
One race worth considering in the early stages is Republican Ron Johnson's Wisconsin Senate seat, which Public Policy Polling finds to be very competitive should Russ Feingold jump in for the Democrats. PPP has Feingold at 50% to Johnson's 41% at this point in a hypothetical rematch of their 2010 contest.
Johnson hasn't proven to be very popular during his first term in the Senate. Only 32% of voters approve of the job he's doing to 40% who disapprove. 28% of voters with no opinion about him also suggests he hasn't made a terribly strong impression on people over the last 4 years. Meanwhile Feingold is still relatively popular despite his 2010 loss. 46% of voters see him favorably to 35% with an unfavorable opinion. That makes him more popular than any other politician in the state who we looked at on this poll.
After the disaster in 2014, it will be great fun to watch a bunch of Republican sweat it out.
Early days, but I'm looking forward to it.