While many of the other Senators who are retiring were facing extremely tough re-election campaigns, recent polls showed Bayh with a 20 point lead over potential Republican opponent former Senator Dan Coats and he had about $13 million in the bank which could have helped him if the race happened to get a little heated closer to election day. Another interesting aspect of this is that despite the fact that Indiana tilts a little bit to the right, Bayh is most definitely a centrist who has wide name recognition which could have helped as many Republicans had been hoping to potential challenge Bayh even though early polls didn't give them much hope. As Chris Cillizza points out, Bayh's retirement really does change things up and could make it much harder for Democrats to hold the seat.
Without Bayh, Democrats may look to their congressional delegation where Reps. Baron Hill, Brad Ellsworth and Joe Donnelly are likely to take a look at running.What's also worth pointing out is that there are still more Republican members of the Senate retiring than Democrats. When you combine that with the fact that Bayh had a large lead in the polls and a huge campaign warchest, the Republicans would most definitely be wrong to spin this into an example of populist anger at Democrats. That simply isn't the case here and the overall situation still suggests that Republican incumbents have just as much to be worried about as incumbent Democrats.
It's not clear whether the Republican field will grow. While national Republicans had rallied around Coats in recent days, the party may well take another run at Rep. Mike Pence who considered a challenge to Bayh before bowing out late last month.
No matter how the two fields shake out, holding the Indiana seat just got much harder for Democrats. Although President Barack Obama won the Hoosier State narrowly in 2008, it is generally regarded by strategists of both parties as swing territory with a slight edge for Republicans. The national playing field's tilt toward Republicans makes the seat all the tougher for Democrats to hold.