In recent years, Republicans have made inroads into the overwhelmingly Democratic constituency of American Jews. But this year, Republican Jews — or Jewish donors to the Republican party, at least — are abandoning their party’s nominee at a stunningly high rate. In 2012, 71 percent of the $160 million that Jewish donors gave to the two major-party nominees went to President Obama’s re-election campaign; 29 percent went to Mitt Romney’s campaign, according to our analysis of campaign contributors, which used a predictive model to estimate which donors are Jewish based on their names and other characteristics. This ratio of support...