So says polling guru Nate Silver:
We are now running about 40,000 Electoral College simulations each day. In the simulations that we ran on Monday, the candidate who won Ohio won the election roughly 38,000 times, or in about 95 percent of the cases. (Mr. Romney won in about 1,400 simulations despite losing Ohio, while Mr. Obama did so roughly 550 times.)
Whether you call Ohio a “must-win” is a matter of semantics, but its essential role in the Electoral College should not be hard to grasp.