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(RNS) — For what is almost certainly the first time in American political history, a relatively small number of Jewish voters may determine which party wins majorities in both houses of the U.S. Congress.

But an internal family dispute could play a major role in how they vote.

In several highly contested U.S. Senate races and a half-dozen House races nationwide, American support for Israel has bitterly divided this tiny electoral cohort, representing 2.4% of the American population.

“Jews, though small in number, have an outsized impact on American elections,” said Jonathan Sarna, a Brandeis University professor who has written extensively on American Jewish history, owing to their high percentage of voter participation, and political giving.

“This election sees Jews divided between those who put their Jewish allegiance first and will therefore not vote for anti-Israel or perceived anti-Semitic candidates, and Jews who…