I think you'll see a drop in support for Obama as you did for Carter, but unless it's based on issues other than Israel, it won't necessarily last. The Democrat party isn't anti Israel, they're simply pro appeasement, whether it's Israel or the US. Younger voters particularly, Jewish or not, I think they're more concerned about economic issues, that's where the focus should be.
I suggest you spend some time lurking at DU when the subject is the Gaza Flotilla. The thinly veiled anti-semitism permeates the conversation, and the number of deleted messages is unusually high. The Palestinians are always portrayed as the victims, and the Israeli military as soulless killers of innocent women and children.