Over 44 painstakingly scripted minutes on the floor of the Senate on Thursday, the majority leader, Chuck Schumer, spoke of his Jewish identity, his love for the State of Israel, his horror at the wanton slaughter of Israelis on Oct. 7 and his views on the apportionment of blame for the carnage in Gaza, saying that it first and foremost lay with the terrorists of Hamas.

Then Mr. Schumer, a New York Democrat and the highest-ranking elected Jew in American history, said Israel’s prime minister, Benjamin Netanyahu, was an impediment to peace, and called for new elections in the world’s only Jewish state.

The opposition was not nearly so painstaking.

Within minutes, the House Republican leadership demanded an apology. The Senate Republican leader, Mitch McConnell of Kentucky, using Mr. Netanyahu’s nickname, declared: “Make no mistake — the Democratic Party doesn’t have an anti-Bibi problem. It has an anti-Israel problem.” And the Republican Jewish Coalition proclaimed that “the most powerful Democrat in Congress knifed the Jewish state in the back.”

The months that have followed the slaughter of Oct. 7 and the ensuing, calamitously deadly war in Gaza have been excruciating for American Jews, caught between a tradition of liberalism that has dominated much of Jewish politics and an anti-Israel response from the political left that has left many feeling isolated and, at times, persecuted.

But Mr. Schumer’s speech was potentially a watershed moment in a much longer political process, pursued initially by Republicans but joined recently by left-wing Democrats — to turn Israel into a partisan issue. Republicans, as they see it, would be the party of Israeli supporters. Democrats, as the rising left would have it, would be the party of Palestine.

At the root of that divide is a fundamental question: Is support for the Jewish State separable from the support of Israel’s democratically elected government? For years, Republicans have said no. Increasingly, the Democratic left agrees but from a different perspective: Israel is bad, regardless of who governs it.