The Cook Political Report (subscription-only) has lowered its prediction for the number of Senate seats Republicans will pick up on Tuesday from 7-9 to 6-8:

While it is becoming increasingly likely that Republicans will hold all 18 of its own seats, Democrats' prospects in three of their 19 seats have improved in recent days. Sens. Barbara Boxer in California and Patty Murray in Washington now appear to be headed for re-election, albeit by small margins. In the special election in West Virginia, Democratic Gov. Joe Manchin now holds an advantage.

While the gold-standard prognosticator has not changed any of its Senate race ratings of late, it has incorporated new polling in the states listed above. The chances that Republicans will win a majority in the Senate, the site continues, are "now non-existent."