The very trenchant political analyst, Larry Sabato, notes that the Republican brand has been harmed recently; but, even so, control of the Senate appears to be up for grabs: Sabato shows the Democratic count at 50 (which includes Safe Democratic, Likely Democratic, and Leans Democratic), and the Republican count at 48 (with the same categories), and two races as tossups (in Alaska and Arkansas).
The Democrats have made gains in Louisiana and North Carolina, what with Mary Landrieu and Kay Hagan now edging ahead. (Sabato has both of these races in the Leans Democratic category now, rather than as tossups.)
And Georgia has now migrated from the Likely Republican category to Leans Republican.
On the other hand, Kentucky remains in the Likely Republican category, despite the problems recently experienced by its senior senator (and Senate Minority Leader) Mitch McConnell. And Montana--which has been in the Leans Republican column--remains there.
Here is the link: http://www.centerforpolitics.org/crystalball/articles/after-the-shutdown-republicans-sort-through-the-wreckage/