Roll Call reports:
Sen. John Ensign is expected to announce at an afternoon news conference in Las Vegas that he will retire rather than face a brutal 2012 re-election campaign, according to knowledgeable sources.
We'll know how knowledge those knowledgeable sources are within the hour: Ensign has a press conference scheduled for 3:00p.m. eastern time.
So far, two Republicans--Kay Bailey Hutchison (Tex.) and Jon Kyl (Ariz.)--have announced their plans to retire, as have five Democrats: Jim Webb (Va.), Jeff Bingaman (N.M.), Kent Conrad (N.D.), and Joe Lieberman (Conn.), Daniel Akaka (Hawaii).
Update: Ensign has announced his plans to retire. The decision is probably a net-positive for Republicans as the outgoing senator had plenty of baggage due to a sex scandal. But keeping the seat is no sure thing for Republicans: Nevada is a battleground state, and the state's Republicans may very well find a way to screw up this election as they did in 2010.