Some excerpts from his March update :
The Senate class of 2012 is substantially Democratic, with Democrats holding 23 seats to the Republicans’ 10. Obviously, this gives Republicans a leg up in contesting seats. The GOP has a small number to defend, while Democrats will have to cover a broad map, and depend on President Obama for long coattails.
...there are seven toss-ups at the moment, six of them Democratic: incumbents Claire McCaskill (D-MO), Jon Tester (D-MT), Ben Nelson (D-NE), Sherrod Brown (D-OH), and the seats of the retiring Jeff Bingaman (D-NM), John Ensign (R-NV), and Jim Webb (D-VA).
In addition to Bingaman and Webb, three more Democratic incumbents have chosen to step down: Daniel Akaka (D-HI), Kent Conrad (D-ND), and Joe Lieberman (D/I-CT). Democratic Senate leaders believe the rest of their incumbents are running again—though surprise retirements can never be ruled out (Sen. Herb Kohl of Wisconsin is a prime example). The three Republican senators to have announced that they are stepping down are Arizona’s John Kyl, Texas’s Kay Bailey Hutchison, and scandal-drenched John Ensign of Nevada.
The North Dakota seat is very likely to switch to the GOP, and Republicans have a clear edge to hold Arizona and are certain to retain the Texas seat. The Hawaii and Connecticut seats will probably stay Democratic. Two currently Democratic seats start off as toss-ups, New Mexico and Virginia, along with the Republican open seat in Nevada. The identity of the eventual party nominees and the coattails from the top-of-the-ticket presidential race may well determine the winners in these three states. President Obama’s support, or lack thereof, could also have a great influence on the contests in Hawaii, Massachusetts, Michigan, Missouri, Montana, Nebraska, and Ohio.
There are eight seats currently leaning to one or the other party. Six are Democratic and two are Republican. Of the eight, the seat of Scott Brown (R-MA) may be the most endangered, initially—although we believe some are underestimating his ability to win a full term despite the state’s heavily Democratic tilt.
The remaining 18 seats are “likely” or “solid” for the twelve Democrats and six Republicans who occupy them.
Depending on the party identity of the Vice President elected in 2012, Republicans will need to win a net three or four Senate seats from the Democrats to take control of the upper chamber of Congress. With six Democratic toss-ups to just one Republican toss-up, the GOP can obviously win the Senate in theory—but it is far too soon to say whether theory will become reality. Just remember how many Senate surprises there were in the primaries and general election of 2010.