As you and others have pointed out, Casey won't be nominated because Democrats biggest beef with Santorum is on abortion, so liberals will pour in money for a pro-choice candidate, not Casey.
No, our biggest beef with Santorum is over his view that you have no right to privacy and that homosexuality is equivalent to bestiality.
Liberals would not vote Santorum over a pro-Life Democrat in the general...but a pro-life Dem would certainly have trouble winning the primary unless the opposition were very much divided.
