In the 2000 election, everyone said the Reps would maintain control of the Senate where they had a 55-45 majority.
What happened? - The Reps lost 5 senate seats and control of the senate to the shock of all the "talking heads".
Even more shocking was that Bush won the presidency without carrying California. Chew on that.
I do think that the battle ground Senate states will have higher turnout and will be close races.