Palestinian protesters gather as sporadic clashes with Israeli forces break out Tuesday near the border fence between the Gaza Strip and Israel. (Mahmud Hams/AFP/Getty Images)

ISRAEL AND Hamas have fought three wars in the Gaza Strip over the past decade, and though it may not look like the others, a fourth one is now underway. Having tried and failed to defeat Israel with rockets and armed cross-border attacks, Hamas this spring deployed a new strategy: assembling thousands of nominal civilians to march on and attempt to breach the border fence, in the calculation that many would be killed. The result would be a moral and political defeat for Israel — and perhaps some relief for a regime that is literally besieged from all sides.

On Monday, this cruel and cynical tactic paid off, albeit at enormous human cost. By the Israeli account, Hamas assembled some 40,000 people at 13 points along the border, then sent groups of them toward the fence, armed with wire cutters, slingshots, knives and, in a couple of cases, firearms. They were met with clouds of tear gas, but when that failed to disperse them, Israeli snipers opened fire. At least 60  Palestinians were killed. On Tuesday, Israeli officials said two dozen had been identified as militants of Hamas or the Islamic Jihad.

On cue, condemnations of the government of Benjamin Netanyahu poured in. Israel was accused of carrying out a “bloodbath” by Human Rights Watch, while Amnesty International said its soldiers may have committed war crimes. European governments summoned Israeli ambassadors and called for an investigation; at Poland’s urging, the U.N. Security Council observed a moment of silence for the victims. Only opposition from the Trump administration likely prevented a Security Council condemnation of the Jewish state.

With the White House’s strong support, Mr. Netanyahu will likely shrug off the international onslaught. He shouldn’t. As the Palestinians well understand, Israel can ill afford further damage to its standing. Sympathy for it is dangerously eroding on U.S. campuses and among Democratic voters — not to speak of in other Western countries. President Trump’s embrace of controversial pro-Israel initiatives, such as the move of the U.S. Embassy to Jerusalem, may in time produce its own backlash.

The question for Israelis is why their government, with weeks of warning about what Hamas would attempt, did not develop a strategy to defeat the operation by minimizing the loss of life. Clearly the government must defend its borders; if it had allowed thousands of Palestinians to pour across toward nearby Israeli communities, the bloodshed could have been much greater. But it seems likely such a breach could have been stopped without such extensive use of lethal force. That impression is only strengthened by the stridency with which senior Israeli officials defended the killings and even called for more. Public Security Minister Gilad Erdan on Tuesday proposed the assassination of Hamas’s leaders.

In fact, Israel can ill afford to escalate, given the low-grade war it is already fighting with Iran in Syria. Most likely it will watch as Hamas reaps the gains of its strategy: Egypt already has responded by relaxing its own closure of the Gaza border. Unbothered by the death toll, Hamas leaders say the marches will continue — which means Israel needs to find a way to stop them without being defeated by them.