Fox News reports Sen. Evan Bayh, D-Ind., is not planning to seek reelection, opening up a significant opportunity for Republicans to pick up a Midwestern Senate seat:

Indiana Sen. Evan Bayh will not seek re-election this year, an unexpected decision that comes on top of other high-profile Democratic retirements. 

The two-term senator is known as a moderate Democrat. His retirement gives Republicans yet another opportunity to pick up a seat in a year when several incumbent Democrats are considered vulnerable and some have already decided to jump ship. 

Connecticut Sen. Chris Dodd and North Dakota Sen. Byron Dorgan both announced their retirements in January.  Democrats are trying to defend open seats in Delaware and Illinois as well. 

Former GOP Sen. Dan Coats had been planning to challenge Bayh in November. But a senior Democratic source told Fox News that recent polling showed Bayh way ahead of Coats, and that the retirement must have been a personal decision. 

Bayh's staff said the latest polling showed Bayh ahead of Coats by 20 points.