David: Since the difference between those two poll results is statistically meaningless, I see no reason to conclude that Casey’s real lead is slipping. As for the ads, they’re disingenuous — especially the immigration ad, which connects Casey to McCain to burnish centrist credentials while suggesting that this puts him to the right of Santorum — but I’m not sure they won’t be effective with voters who aren’t paying close attention. I doubt the Schiavo position hurts him with many people who aren’t already solidly in Santorum’s camp, and standing silent seems like a reasonably smart way of handling the abortion issue (a pro-choice campaign, besides being a complete flip-flop, would fire up Santorum’s support, but running as an unapologetic pro-lifer would depress Democratic turnout). I’m not saying Santorum can’t win, but that’s not the way I’d bet.