Richelieu's analysis seems compelling:
I think in the long run a Robertson endorsement will prove a very mixed blessing. First, it will put Rudy and abortion in the spotlight. Rudy's pro-choice record remains pro-choice, whether or not Pat Robertson is now pleased with it. Second, the more pro-life-centric candidates will see this endorsement as a blatant attempt at a daylight robbery of "their voters" by Rudy and his New York heist crew. They won't take that sitting down. Much like a brazen attempt by the Chicago "Outfit" to take over the Gambino and Lucchese rackets in Brooklyn and Queens, the other candidates cannot sit still for this. Now the knives will come out and a serious grind on Rudy's stand on social issues will begin. Look for paid ads and mail telling primary voters many things they still do not know about Rudy Giuliani.
Third, Robertson is at heart a carny and a flake. Rudy will now have to wear him like a hat, gathering unwelcome media attention. This endorsement may prove to be the Balkan pistol shot of 1914 that sparks the final explosive phase of the primary campaign. It is an audacious move by Rudy and will be either a big milestone in Giuliani's path to the nomination, or the one step too far in his risky tango with the abortion issue.
Bill Kristol and Daniel Larison are thinking along similar lines. (And how often do you get to write that sentence?) But all of that said, if Rich Lowry's source is right and "there's plenty more where this comes from" (social-con endorsements for Rudy, that is), then the other candidates better get their knives out quickly. The longer they wait, and the more primary voters are told, by Robertson and by others, that it's okay to be pro-life and pro-Rudy, the harder that notion will be to dislodge.