AEI finds evidence -- even before the Democratic convention and its fumbles on Jerusalem as the capital of Israel -- that Jewish support for Obama has dipped considerably. While the percentage of  Jewish voters and their impact has been greatly diminished over the years, this time the dip could be meaningful in several swing states:

What all these results point to is something less than a two-to-one advantage for Obama over Romney among Jewish voters, similar to the split in the Jewish vote in 1972, 1976, 1984, and 1988.  The drop-off in the Democratic percentage among Jews could be crucial, as the Republican Jewish Coalition points out, in target states like Florida, Pennsylvania, Ohio, and Michigan-particularly Florida, where in 2008 Obama carried the heavily Jewish Broward and Palm Beach Counties by 390,145 votes, much more than his statewide margin of 236,148.  In other words, without the size of his margin in those counties, Obama would likely have lost Florida's electoral votes.

There is always a tendency to ascribe changes in Jewish voting patterns to issues relating to Israel.  Dissatisfaction with incumbents' Israel policies undoubtedly accounts for the very weak Jewish support, compared to other Democrats, of Jimmy Carter (45 percent) and the record low support for George H. W. Bush in 1992 (11 percent).  But responses to issue questions in the AJC surveys suggest that while some of the decline in Obama's standing is prompted by Israel issues, some is due more to economic and other issues on which Obama has had problems with voters generally.  

It should be noted that these polls (except for IBD/TIPP) were conducted well before the Democratic National Convention, at which reference to Jerusalem as the capital of Israel was first omitted from the platform, then awkwardly reinserted, and before Israeli Prime Minister Benjamin Netanyahu's recent statement on red lines and red lights.  The bottom line: it looks like Jewish voters will favor Obama by a little less than two to one, and not, as in 2008, by a little less than four to one.

h/t: RL