This article by William Galston in The New Republic has assembled the most recent polling data. Viola, he shows that the Senate is in play.
If you bet favorites to win, you'd still bet on the Dems having a slight majority when the new Senate begins in January of 2011. But as these polling numbers show, the outcome is likely to be very close and the GOP might possibly achieve a narrow majority.
A key issue that Galston doesn't mention is the intensity variable. This year Republicans are excited about voting and Democrats are not. In non-presidential elections like this one voter turnout is crucial, and is much influenced by intensity, the desire to vote.
I am reminded of a pet peeve of my late father, a lifelong southern Democrat. He believed Republicans typically turn out to vote in larger numbers than do Democrats. I suspect he was right.
