Democratic Sen. Evan Bayh of Indiana won't run for reelection

Bayh cited the lack of bipartisanship on Capitol Hill as his main reason for leaving, adding to skepticism that the fractiousness in Washington can be repaired and undermining President Obama's efforts to build bridges.

"There is too much partisanship and not enough progress -- too much narrow ideology and not enough practical problem-solving," Bayh said in a statement. "Even at a time of enormous challenge, the people's business is not being done."

His announcement in Indianapolis came amid Democrats' rising anxiety about the party's national standing, especially among independent voters who tend to identify with middle-of-the-road Democrats such as Bayh. A growing anti-incumbent mood fueled Republican Scott Brown's victory last month in a special election for the Senate seat long held by the late Edward M. Kennedy, one of the chamber's stalwart liberals. Democrats were defeated in the 2009 gubernatorial races in Virginia and New Jersey. And senior Democratic Sens. Byron Dorgan (N.D.) and Christopher J. Dodd (Conn.) announced recently that they will not run for reelection.