This pick would help with conservatives and give McCain help in Virginia but Jewish voters are as stuck on the Democrat plantation as blacks. Doubt any large Jewish defections.
Obama is already doing terribly among Jews, for a Democrat. Whereas any other Dem usually gets at least 80%, Obama would probably be lucky to grab 60% at best. McCain will win a lot of Jewish votes who would have gone to Hillary. GOP candidates drawing unusual high numbers of Jewish votes aren’t without precedent. Both Ike and Reagan won 40-50 %, Bush 2004 36% (Bush 2000 10% or even less... but remember Lieberman was Gore’s running mate).