If the GOP doesn’t win a bunch more than 6 seats this time they’re not likely to keep the Senate in 2016. They need to win a big buffer to be able to hold off the Dems in 2016 when the GOP will be defending 24 seats to the Dems 10... and 7 of the GOP’s seats will be in blue states that Obama carried in 2012.
I think in 2016 a whole lot of those Demon Rat states will be sorry they voted for Obama.