Former Sen. Evan Bayh will run for the Senate after all , buoying Democrats’ chances of winning the open seat in Indiana and the Senate majority.  

The news, first reported by CNN’s Tom LoBianco , is surprising considering Bayh, who didn’t seek re-election in 2010, had shown no interest in running, despite Democratic recruitment efforts earlier in the cycle. The Democratic nominee, former Rep. Baron Hill, stepped aside on Monday to allow the state party to replace him on the ballot.   

Hill wasn’t raising the money necessary for a top-tier campaign against GOP Rep. Todd Young in the race to replace Republican Sen. Dan Coats, who is retiring, but Bayh’s entry immediately changes the dynamic.  

We’re changing The Rothenberg & Gonzales Political Report /Roll Call rating from Republican Favored to Tilts Democrat .  

Bayh won’t have a lot of time to shake off any rust from his campaign apparatus since he hasn’t been on the general election ballot since 2004. But if he was initially turned off by a long campaign, Bayh now has a four-month sprint to November with more than $9.2 million sitting in his campaign account, so he won’t have to spend as much time raising money.  

“He shakes it up,” said a GOP source in the state. “He left six years ago in a very classy way by attacking the system — Republicans and Democrats.”  

Of course, Republicans won’t give him a free pass. They’ll bring up his votes for President Barack Obama’s health care law, his overall voting record with Obama (including the so-called stimulus bill), his lack of effectiveness while in the Senate, and his lobbying record after he left.   

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Republicans will also highlight the lack of time he has spent in Indiana, including his expensive homes in the Washington, D.C., area and Florida. (Residency was a key factor in Sen. Richard Lugar’s fall in the GOP primary in 2012.) And Bayh, a former two-term governor and son of a senator, will be portrayed as a lifelong politician.  

But Indiana voters don’t automatically know, believe, or remember the negative parts of Bayh’s background. Republicans will have to litigate that case in the coming months. The bottom line is that Indiana is now firmly in the list of competitive states that will decide the majority and require considerable spending from the GOP side that the party previously would not have had to spend.