(CNN) - Sen. Evan Bayh, D-Indiana, announced Monday afternoon that he will not seek a third term in the Senate - a major blow to Democrats worried about losses in the looming midterm elections.
"Congress is not operating as it should," Bayh said at a news conference in Indianapolis. There is too much partisanship and "the people's business is not getting done."
Bayh said he loves public service, but does "not love Congress" and is "not motivated by strident partisanship or ideology."
He cited the Senate's recent failure to pass a jobs bill and legislation that would have created a deficit reduction commission as evidence of what he characterized as a broken political system.
Bayh, a former two-term governor, was first elected to the Senate in 1998, taking 62 percent of the vote. He won re-election with 64 percent six years later.
Bayh is the third Democratic senator to announce he is retiring when the curtain drops on the 111th Congress. Sens. Chris Dodd of Connecticut and Byron Dorgan of North Dakota previously announced they would not seek re-election.
In total, Democrats will have to defend five open seats in November, as Roland Burris of Illinois and Ted Kaufman of Delaware have stated they will not run for their own six-year terms. Burris was appointed to President Barack Obama's former Senate seat, while Kaufman was appointed to Vice President Joe
Meanwhile, Republicans will be forced to defend six seats in the midterm elections. Sens. Judd Gregg of New Hampshire, Kit Bond of Missouri, Jim Bunning of Kentucky, George Voinovich of Ohio and Sam Brownback of Kansas are all retiring at the end of the year.
Sen. George LeMieux of Florida - who was named to replace Sen. Mel Martinez, who resigned before the end of his term - also will vacate his seat.
Dan Coats, former Republican senator, recently announced a bid to challenge Bayh this year. Coats served from 1989 to 1999, but chose not to run for re-election in the 1998 contest that Bayh won. Former Rep. John Hostettler and state Sen. Marlin Stutzman also are bidding for the GOP Senate nomination
Even though Bayh, a political centrist, probably would have faced a difficult re-election battle due to the anti-incumbent political climate, an Indianapolis Star/WTHR poll conducted in November indicated that 61 percent of Indiana voters approved of the job Bayh he was doing, while only 24 percent
One source said Bayh could consider another bid for Indiana governor.
But he "hates the Senate (and) hates the left bloggers," said a friend of the senator who has also served as a longtime adviser. "They are getting their wish (of) pure Democrats in the minority."
A Democratic Party source told CNN that Bayh's announcement took national Democrats by surprise. The source added that Democratic Reps. Baron Hill and Brad Ellsworth and Evansville Mayor Jonathan Weinzapfel may all consider making bids for the Democratic Senate nomination.
Bayh, a centrist Democrat, was considered a possible running mate for Obama in 2008. Bayh's father, Birch, served three terms in Senate.
– CNN's Mark Preston, Gloria Borger, John King, Paul Steinhauser, Alan Silverleib and Candy Crowley contributed to this report.
Updated: 2:35 p.m.