One more Senator down! John Ensign is finally surrendering to reality today and announcing he won't run for re-election; he had serious problems in both the primary and, if he survived, the general election, so this seems pretty sensible on his part. Recall that, if it wasn't for scandal, Ensign would almost certainly be running for president right now, and might well have had a reasonable chance of winning the nomination.
Nevada is of course a swing state that probably leans a bit to the Democrats. It's possible that Ensign's retirement could even help Republicans hold it, as they were previously anticipating a potentially brutal primary between Ensign and Rep. Dean Heller. On the other hand, given what happened the last time Nevada's Republicans tried to nominate a candidate for the Senate, it's also possible that they'll wind up with a free-for-all and some random guy shooting craps at Caesar's will wind up winning the primary. Which, of course, would be an improvement over Sharron Angle, from their perspective.
Total so far: eight senators are retiring, which is historically high, although not as many as called it quits in 2010. Five Democrats (including Holy Joe Lieberman), three Republicans. And I suppose that it's worth mentioning that three are in the Mountain Southwest (Nevada, Arizona, New Mexico), all in potentially competitive states in the presidential election. The Democrats remain likely to lose seats -- and could lose quite a lot of seats -- in the Senate in 2012, but if it does wind up being a strong year for Democrats, they could break even or even gain two or three seats. If that's going to happen, they'll certainly need Nevada.