Breaking down Romney, Obama in Ohio

The New York Times' Nate Silver reports that Ohio's 18 electoral votes have a 50-50 chance of deciding the presidential election.

So what's the situation there?

For one, Obama is favored.  RCP's poll average of Ohio has the state 47.6% Obama, 45.7% Romney.  Assuming 2% of the electorate vote for someone else, that leaves 4.7% undecided. Seems like a strong lead for Obama.

Obama would have to take 21% of the undecided vote to get to 49%, which may be enough to win.  He would have to win 36% of undecided voters get to 50% overall.

Romney would have to take 49% of the undecided vote to get to 49%, which may be enough to win.  He would have to win 64% of the undecided vote to get to 50% overall.

So Ohio, which should be an Obama win, comes down to which scenario is more likely among undecided voters Does Obama take 21%-36% of their vote, or does Romney take 49%-64% of their vote?

That may sound to most like a lock for Obama, and he's still the favorite to win Ohio, but keep in mind these people still aren't sold on Obama after four years as president, and Romney has strong polling leads with independent voters.  Romney has a strong outside shot of taking Ohio.