Nate Silver posted his latest election forecast for the Senate and he gives the GOP a two in three chance of maintaining control.
Election probabilities after all 35 races are decided. (Dems have 23 seats at risk, GOP has 12)
GOP and Dems end up with 50 seats (VP tiebreaker) - 17.1%
GOP ends up with 51 seats - 15.7%
GOP ends up with 52 seats - 12.3%
All other scenarios where GOP maintains control are less than 10% probability.
Dems take control with 51 seats - 15.6%
Dems end up with 52 seats - 11.0%
All other scenarios where Dems take control are 5% or less
There are so many close races it is likely that we will have surprises on both sides election night. The problem for Democrats is that a loss of just one or two of those 23 seats will make their longshot bid for control even longer.
Say what you want about Silver's prognostication skills, but if you're a serious political junkie, he's got some fascinating graphics.