Sean Trende breaks down the races in order of competitiveness. On the Republican side, Brown (MA) and Ensign (NV) are vulnerable, though Brown appears to be doing better than expected and scandal-ridden senators have definitely won re-election (although David Vitter’s home state is much more conservative than Nevada), while Kay Bailey Hutchinson’s seat is fairly open (though in a presidential year, the GOP candidate could definitely ride coattails).
The Democrats have a lot more vulnerable seats. Nebraska, Nevada, Montana, Missouri, Florida, Virginia, and Ohio are all vulnerable – Trende thinks that North Dakota is virtually a GOP seat at this point. West Virginia, Pennsylvania (I’m skeptical about this one), Wisconsin, Michigan, and Washington are all also vulnerable, depending (according to Trende) on the presidential elections. New Mexico is safe as long as Bingaman stays, and Connecticut, Hawaii, Rhode Island, and New Jersey are safe unless the Republicans pick up someone really good. Linda Lingle, who made brief headlines as a possible moderate VP pick for McCain, could definitely win the Senate seat; I’m less excited about Rell or Carcieri. I’m calling Menendez to be safe. Sure, Chris Christie won in 2009 and has a sky-high approval rating. But look at every other election with a vulnerable Democrat. Why didn’t the GOP win? A party implosion and/or a weak candidate always lost the election in spite of the low Democrat approval ratings (see: Zimmer and Forrester). Tom Kean, Jr. is looking at a rematch, but he lost by 9 points last time around (though he has much better poll numbers this year).
With the seriatim retirement announcements of Republican Senator Kay Bailey Hutchison, Democratic Senator Kent Conrad, and independent Senator Joe Lieberman (who caucuses with the Democrats), the 2012 campaign for Senate has officially kicked off. While the 2010 races were, until fairly late in the game, only about breaking the Democrats’ filibuster-proof majority, 2012 will feature a full-on battle for control of the upper chamber.
While it is still too early to make any real predictions, we can break these seats down into categories of competitiveness. Democrats clearly start out with more vulnerabilities than Republicans, largely as because (a) Democrats have to defend 23 seats to the Republicans’ 10 and (b) of those seats, the median Democratic seat has a PVI of D+2, while the median Republican seat has a PVI of R+8.