The Friends Committee, a Quaker lobbying group, has been pushing in Washington for a cease-fire, going up against more powerful and better-funded groups backing Israel.
George Latimer, the Westchester County executive, told The New York Times he would run against Mr. Bowman, a rising star of the Democratic left, next year.
Representative Summer Lee of Pennsylvania, who joined calls for a cease-fire, has become one of several progressive lawmakers facing new pressure from primary challengers.