Herb Kohl's decision not to seek re-election to the U.S. Senate is another significant blow to the Democrats, coming as a surprise to even Patty Murray, chair of the DSCC. With 23 seats up for grabs compared to 10 Republican seats, it has long been noted that the Republicans should be able to take control of the Senate in 2012. But, with decisions not to run by Webb in Virginia, Conrad in North Dakota, Bingaman in New Mexico, and now Kohl in Wisconsin, Republicans now clearly have a chance to gain not just the 4 seats needed to ensure control of the Senate, but the 13 seats that would give them a 60-vote, filibuster-proof majority. This would be an amazing turn around, given that it was the Democrats who found themselves in this position just 3 years ago.
In order to get to 60 Senate seats, Republicans will first have to retain control of the 10 seats they have up for election, including Brown in Massachusetts and open seats in Nevada and Arizona. Nevada is looking better with Ensign's resignation, but Kyle's decision not to seek re-election places Arizona in the toss up column, particular if Gabrielle Giffords is able to recover and challenge for the seat. Brown is actually looking better in his chance of retaining the Massachusetts seat that he won in a special election. The other seven Republican seats are considered "safe".
Six seats held by Democrats are clearly rated as toss ups--Missouri, Montana, North Dakota, Nebraska, Ohio, and Virginia. Two of these are open seats: Kent Conrad (ND) and Jim Webb (VA) are not running again. Republicans will have to win only 4 of these to get to a Senate majority, but all six, if they expect to have a chance of getting to 60 seats.
In addition to these 6 seats, Republicans would have to win seven additional seats currently held by the Democrats. Republicans should be competitive in the following states where incumbent Democrats would hold a slight advantage: Florida (Nelson), Michigan (Stabenow), Pennsylvania (Casey), and New Jersey (Menendez). Republicans have won the governorships in all 4 of these states in the last election cycle. Finally, decisions by Lieberman in Connecticutt, Bingaman in New Mexico, as well as Kohl in Wisconsin have placed these 3 seats that should have been likely Democrat holds into the competitive category.
Keep in mind also that in 2010, Senate seats in California, Washington, Delaware West Virginia and even New York were also considered up for grabs, and seats from these states are up again in 2012. It is hard to predict at this point which additional seats might be in play. Clearly, however, Republicans should be targetting, recruiting top-tier candidates and raising funds to contest for the 13 seats necessary to get to a 60-seat Senate majority. Only attempting to gain a simple majority in the Senate would be setting Republican sights too low.