Public Policy Polling finds support for Sen. Debbie Stabenow, D-Mich., to be very thin at the moment, pinning her approval rating at just 41 percent. Her disapproval is at just 40 percent, but there could be an opportunity here for Republicans to drive that up with a serious challenge.

Stabenow, who defeated Republican Sen. Spence Abraham in 2000, polls in the low 40s and she only narrowly leads several hypothetical Republican opponents, including Reps. Pete Hoekstra and Candice Miller, and Secretary of State Terri Lynn Land.

Republicans must gain a net of four seats to ensure control of the Senate, although three would be enough if Obama loses re-election. At this early date, their best pickup opportunities for 2012 seem to be Michigan, Florida, North Dakota, Nebraska, Virginia, Montana and Missouri.  Depending on retirements and the political climate, there could also be opportunities in Wisconsin, Pennsylvania, West Virginia, New York, New Mexico and New Jersey.

The GOP will be playing defense  most heavily in Nevada, Massachusetts and Maine, but that's about it. The Republicans were wiped off the map in the 2000 and 2006 Senate contests, so they have little territory to defend.