On the other side of the aisle, two Republican Senators up next year stand out as potentially vulnerable: Sens. Scott Brown (Mass.) and John Ensign (Nev.).
Even with the good ink that he has received, Brown has to be regarded as extremely vulnerable, if only because of his party.
Any Republican holding a federal office in the Bay State is at risk — and Brown in particular since he was elected in a special election. The 2012 electorate will be different from the one that turned out in January 2010, and the presence of Obama on the ballot could both boost Democratic turnout and make the entire election more partisan.
Ensign’s problems stem from his affair with a former staffer, and he could either draw a formidable primary opponent or even decide against continuing his bid for re-election. On the Democratic side, Rep. Shelley Berkley is most often mentioned as a candidate. While she has had no trouble holding her Las Vegas-based, reliably Democratic district, she would not necessarily have such strong statewide appeal.
Beyond those two GOP vulnerabilities, the only obvious Democratic targets are those states where strong incumbent Republicans could face difficult primary challenges from much more conservative opponents. Sens. Olympia Snowe (Maine) and Dick Lugar (Ind.) are obvious examples, though at this point no serious Democrat has come forward in either race.
There are already enough Democratic seats at risk to regard control of the Senate in 2012 as up for grabs. But we aren’t likely to know until at least the end of this year how the cycle is likely to play out, and as is usually the case, unexpected events are likely to play a role in the Democrats’ chances of hanging into their Senate majority.