Here is another one of those embarrassing comparisons to Jimmy Carter. One must go all the way back to 1980 to find a Democratic presidential nominee with worse polling among Jews. Obama got 71% of the Jewish vote in 2008 but is now down to 59% according to a Tripp poll. Carter got only 45% of the Jewish vote in 1980. No Democrat has ever won the White House with that low a share of the vote. The Democratic candidates who scored that low, Carter in 1980, Dukakis, Mondale, McGovern, Adlai Stevenson, were all losers who went on to lose the election.
It's probably better to think of the Jewish vote as an indicator of election outcome rather than a decider however in swing states with large Jewish populations, such as Florida, it could decide the election. Among Catholics Obama has a 2 point lead 46% to 44% another low that compares to Jimmy Carter in 1980.