Top staffers for Senator Fetterman, whose open support for Israel has drawn the ire of his fellow Democrats, are quitting to work for more left-wing candidates and causes, a sign of the growing backlash against liberal politicians who support the Jewish state. 

Mr. Fetterman’s long-time communications director, Joe Calvello, left in March to work for the mayor of Chicago, Brandon Johnson, whom he called in a statement “a true progressive.” Mr. Fetterman’s deputy communications director, Nick Gavio, also left last month, to work for the Working Families Party, which includes members of the left-wing “Squad” in the House. A press and digital aide for the senator, Emma Mustion, is leaving to work on Senator Casey’s re-election campaign.