Not likely but possible, so says Karl Rove:
"Democrats began the year as masters of the political universe, winning the White House and increasing their majorities in Congress. But the year is ending badly for them. Their top initiative, health care, is deeply unpopular. Congress's approval rating is 26%, Speaker Nancy Pelosi's is 28%, and Senate Majority Leader Harry Reid's is an anemic 14%.
Political currents are running against the party of Barack Obama. Democrats now trail Republicans by four points in Gallup's generic ballot poll. In 1994, the year the GOP took control of Congress, it wasn't until March that Republicans took the lead in that poll—and then only by one point and for a short period of time.
With a good environment this election cycle, Republicans have recruited competitive candidates who could turn otherwise close contests into runaway victories, likely defeats into wins or at least close contests that, if things break right, tip to the GOP.
Today, there are only 40 Republicans in the Senate. In January 2011, there could be 44, 46 or more if the party runs strong campaigns in contests that haven't jelled yet, or if some Democrats retire instead of risking defeat."
The Democrats will have no one to blame but themselves if that happens. Oh, and Obama. And Reid. And Pelosi. And Frank, Dodd, Kerry, et al.