You do realize that Obama will campaign somewhere where he is popular in the state (like Philadelphia). You're foolish if you believe his travel to the state hasn't been poll tested to ensure it helps more than it hurts Wolf.
It's more the fact the he will likely appear alongside Wolf and Republicans could cut a final ad linking him to Obama, which could mean just an 8-point win instead of a 18-point win.
This assumes that the people who are voting for Tom Wolf are unaware that he is a Democrat, and that the President is also a Democrat. Corbett could cut his polling deficit in half, but this won't be the reason.