Santorum can win Ohio, but it's an uphill battle. Obama seems pretty popular here. If he could somehow compensate Pennsylvania for Ohio, that would be fantastic.
Six years after Pennsylvania voters showed Senator Rick Santorum decisively (59-41) that they no longer wanted him in the Senate they will still know why they no longer wanted him in the US Senate. There's just no state or combination of states that Rick Santorum or any other Republican candidate can pick up as compensation for the loss of Ohio. You can say "Pennsylvania", "Michigan", "two of Iowa, Minnesota, and Iowa", or for that matter "New York" or even "California" if you wish, but any Republican nominee for President must force a change in consciousness of America to win election.