My opinion of why Santorum lost as a PA voter? Combination of factors. 1. He completely pissed off the hard-core conservatives by backing Specter in 2004. If Specter had won the primary over Toomey by 20 points, nobody would have held a grudge, but Toomey lost by 2 damn points, and many of us are still bitter.
2. He says a lot of wacky religious things, which irritate us non-religious types. My brother is a hard-core conservative as it comes, but he voted for Casey! When asked why, he said, "Santorum is kind of a wacko..."
3. Many see him as a faux conservative. He's the number 3 man in the Senate, so if the Senate is a wishy-washy bunch which is not advancing the conservative agenda, he's gotta bear some responsibility. I called his office after HR 2611 passed and the Mexicans were taking to the streets. I wanted to know his stance on HR 2611. The woman said, "The Senator has no position at this time, however, you are free to tell me your position...." Boom, a month later he's against immigration. If he thought he could have gotten away with it, he would have been on the Bush-open borders team, but couldn't with the election coming up. He might as well have, then he could have lost 62-38, instead of 59-41.
That being said, I voted for him, even made some phone calls on his behalf. He is a far better Senator than Bob Casey will be.