If you missed it yesterday, AT's Rich Baehr had a great piece on the prospects for 2012 in the senate over at Pajamas Media.

The huge problem for Senate Dems is that if they vote with the president on taxes, they will likely get a primary challenge from the left. If they vote against the tax bill, they hand their GOP opponent a potentially devastating issue in the general election:

At least ten of the Democratic incumbents already looked vulnerable at the start of the 2012 cycle: Sherrod Brown in Ohio, Herb Kohl in Wisconsin, Claire McCaskill in Missouri, Robert Menendez in New Jersey, Ben Nelson in Nebraska, Bill Nelson in Florida, Debbie Stabenow in Michigan, Jon Tester in Montana, Jim Webb in Virginia, and Kent Conrad in North Dakota. Some analysts might throw in Bob Casey in Pennsylvania. Joe Lieberman is a unique case. It is not clear on which ticket he will try to run in 2012. If he runs as a Democrat, he will surely face a left-wing challenger, and could lose the primary as he did in 2006.

Evidence of the threat to these senators is the early activity on the Republican side in several of these races, with multiple candidates showing interest in a few of the states, and strong GOP challengers already emerging in Florida, Missouri, and Nebraska.

If the Democratic incumbents were assured they would be re-nominated, they could begin to position themselves early on for their re-election fight and move a bit towards the center to improve their chances with independents. Independent voters broke sharply for the Republicans in the 2010 midterms, with one of every three independents who voted with the Democrats in 2008 moving to the GOP in 2010. But there are now looming threats from the progressive wing of the party if some of these incumbents are seen as straying from the ideological path favored by the left on the tax bill.