What does Israel plan to do about its years-long conflict with Hamas in Gaza? Benjamin Netanyahu told foreign envoys this morning that his strategy remains “forceful deterrence,” but that’s not his only option. Another “open possibility” might be total conquest, Netanyahu warned:

Prime Minister Benjamin Netanyahu says Israel is pursuing “forceful deterrence” against Gaza’s Hamas rulers and does not rule out a further escalation.

Meeting with foreign ambassadors on Wednesday, he said “you can either conquer them, and that’s always an open possibility, or you can deter them.”

“We are engaged right now in forceful deterrence, but I have to say, we don’t rule out anything.”

Later in the video, Netanyahu hailed Winston Churchill’s leadership in World War II as a model. When the Nazis sent thousands of rockets into London, he reminded the diplomats, Churchill’s response was to “level” German cities as a proportionate retaliation. “I don’t criticize [Churchill] for anything,” Netanyahu said, “but this is not our response.” He said that Israel would continue to use “surgical methods” to “prevent collateral damage,” but that the world shouldn’t expect zero civilian deaths in a war where Hamas is “deeply embedded” among civilians.

That warning about possible conquest of Gaza will increase pressure on Joe Biden to find a way to bring the war to a halt. Biden has been trying to encourage Israel to seek a cease-fire, but thus far Hamas hasn’t seemed too interested in ending its rocket fire even temporarily. Israel, which stopped short of a serious ground invasion in 2014, would probably prefer not to conduct urban warfare in Gaza, with its attendant casualties, captures and hostaging, and so on. However, the decade-plus of rocket fire is clearly untenable, which is why Netanyahu now has put military conquest back on the table.

That’s a problem for Biden diplomatically, but also politically at home. The war with Hamas has split his party, and the divisions are already becoming bitter:

Many Democrats remain staunchly supportive of Israel and the actions it says it must take in self-defense. But as a growing number of Democrats urged a cease-fire over the past week, Biden for days refused to join them, waiting until after his third conversation with Prime Minister Benjamin Netanyahu to cautiously support such a move. …

Changing Democratic attitudes have been evident across the country in recent days. Rep. Cori Bush, a freshman Missouri Democrat and Black Lives Matter activist, delivered an impassioned speech on the House floor, promising to “fight for our rights in Palestine and in Ferguson,” tying the conflict in the Middle East to battles for racial justice at home.

Sen. Bernie Sanders (I-Vt.), who in recent years has become one of the most prominent elected officials among liberal Democrats, penned a widely circulated op-ed lambasting the Democratic leadership for being too accommodating toward Israel. “Palestinian lives matter,” he wrote in the New York Times.

Even longtime Israel hawks such as Senate Majority Leader Charles E. Schumer (D-N.Y.), Senate Foreign Relations Committee Chairman Robert Menendez (D-N.J.) and House Judiciary Committee Chairman Jerrold Nadler (D-N.Y.) have shown a sensitivity to the shifting winds in their party with carefully worded comments suggesting they would not always march in lockstep with the Israeli government. All three have a strong Jewish presence in their constituencies.

Biden’s decision to proceed with an arms sale to Israel is exacerbating this split:

A $735 million weapons sale is exposing fault lines in the Democratic Party over what to do about escalating violence in Israel, splitting party leaders who remain solid allies of Israel and more progressive Democrats who see Israel’s treatment of Palestinians as a social injustice.

Democratic leaders have paved the way for the sale of joint direct attack munitions, which the Israel Defense Forces can use to make precision strikes, despite the outrage the sale is provoking among progressives. …

The administration notified lawmakers on May 5 that it had approved selling Israel $735 million in weapons, mostly of Boeing-made Joint Direct Attack Munitions that can turn so-called dumb bombs into precision-guided missiles.

More broadly, progressives, including some in positions of power such as House Defense Appropriations Subcommittee Chairwoman Betty McCollum (D-Minn.) and Senate Budget Committee Chairman Bernie Sanders (I-Vt.), are increasingly pushing to place more conditions on or revisit the $3.8 billion in military aid the United States sends Israel annually.

Biden has been almost entirely reactive in his first four months, in pretty much every policy area — except this, so far. Perhaps he senses that progressives really are out of step with most Americans on this issue, which is very much the case. Or perhaps Biden understands that if drug cartels started shooting Iranian rockets into El Paso from Juarez, the progressives would be singing a much different tune. That is pretty much Netanyahu’s point here too, and it’s tough to argue with it. That means Biden will have yet another break with progressives, and this one might not be easy to paper over.