In the House, Democrats elected in Republican-leaning districts in 2008 with the help of a heavy Democratic turnout fueled by Obama's candidacy are struggling to hold their seats in the face of a growing Republican wave.
The fate of first-term Democratic incumbents like Virginia's Tom Perriello, Colorado's Betsy Markey, Ohio's John Boccieri, and Florida's Alan Grayson could be crucial to the balance of power.
In the Senate, a handful of veteran Democrats facing unexpectedly tough re-election races could decide the outcome, including Democratic leader Harry Reid of Nevada, Russ Feingold of Wisconsin, Patty Murray of Washington, and Barbara Boxer of California.
Democrats are keeping an eye on two election 2010 races they thought would be cakewalks, the Connecticut battle for retiring Democratic Senator Chris Dodd's seat and the election to replace late West Virginia Senator Robert Byrd.
If Republicans pull a surprise win in either state it could be the end for Democratic Senate hopes.
