I'm not so sure. I haven't seen any number to suggest the Jewish vote is fragile. The vast majority of American Jews are quite liberal and don't seem to care about Israel nearly as much as socialist politics. (not all just most). I think Obama's polls are showing the loss of the Jewish vote as a result of his anti-Israel policies has been inconsequential and he felt emboldened. I could be wrong, you may be right that it was just a typical Obama F-up.
But Romney is a liberal and they know it! I live in a heavily Jewish suburb of Philadelphia. The Jewish people I know were leaning Romney. They were a little upset about the selection of Ryan as VP, but even so the only thing that could really pull them back to Obama would have been if Hillary were to run as has Veep.
The Jewish people I know are all folks who voted for O last time. My wife just talked over the fence with our (Jewish) Hillary loving neighbor. She was in tears about what's happening with our country after the whole Israel thing last night. She had told me before that she was voting Romney this time (last time she had an Obama sign in her yard and on her car). The woman was in tears over the antics last night. No way Obama's getting her back.