I think you are wrong. It seems to me that it was pretty close. I will have to go back and look at that election cycle, and can't do so tonight.
From memory, and I appreciate your indulgence and corrections, the Toomey/Specter primary was close, and that is where the President weighed in. The justification for supporting Specter was that the President always supports incumbents, and that is a good rationale. But the President does not support all incumbents. The President wanted Specter to win the primary.