Now some Democrats are testing the boundaries of what has been the politically acceptable position on Israel in the mainstream parties. They include Ilhan Omar, a Somali-American Muslim running for an open House seat in Minneapolis; Rashida Tlaib, a Palestinian-American Muslim running in Detroit; Ms. Ocasio-Cortez, running in a heavily Democratic district in the Bronx and Queens; and Leslie Cockburn, co-author of “Dangerous Liaison: The Inside Story of the U.S.-Israeli Covert Relationship,” who is running in a Republican-leaning district in Virginia. None of them would comment for this article.

They have not made their views on Israel a central issue of their campaigns, but they also have not held back. Ms. Tlaib, in an August interview with the liberal magazine In These Times, endorsed a one-state solution that could jeopardize Israel’s status as a Jewish state.

“It has to be one state,” she said. “Separate but equal does not work.”

Ms. Omar, who had criticized Israel’s “evil doings” in 2012, was accused on Twitter of anti-Semitism after her campaign got underway. “Drawing attention to the apartheid Israeli regime is far from hating Jews,” she responded.

Against a backdrop of a White House that has taken a series of measures explicitly targeting Palestinians — moving the American Embassy from Tel Aviv to Jerusalem, slashing aid and most recently, closing the Palestine Liberation Organization office in Washington — the group’s stances are at odds with several prominent pro-Israel party leaders, setting up an interparty conflict often waged over generational lines. Republicans have already lobbed charges of anti-Semitism.

“I do worry that there are some on the extreme left of our party who adopt slogans” that are creating tensions, said Representative Brad Sherman, Democrat of California and a pro-Israel voice in the party.