Kamala Harris is in a bind. Despite rallying Democrats behind her, she’s still being heckled by protesters who want to end U.S. support for Israel’s war in Gaza. Many of those activists want her to endorse an arms embargo against the Jewish state. Her chief foreign policy adviser, Phil Gordon, has ruled that out. But a flat refusal risks alienating progressives in key states like Michigan and sparking an ugly confrontation at this week’s Democratic convention.

There’s a solution that allows Ms. Harris to go beyond merely calling for a cease-fire and saying that “far too many” civilians in Gaza have died. Without supporting an arms embargo, she can still signal a clear break with Joe Biden’s near-unconditional support for an Israeli war effort that many legal scholars believe has led to genocide. And she can do so in a way befitting a former prosecutor: When it comes to Israel, Ms. Harris should simply say that she’ll enforce the law.

The law in question has been on the books for more than a decade. It prohibits the United States from assisting any unit of a foreign security force that commits “gross violations” of human rights. Aid can be reinstated if the foreign country adequately punishes the perpetrators. Passed by Congress in 1997, it bears the name of former Senator Patrick Leahy — and it has been applied hundreds of times — including reportedly against U.S. allies like Colombia and Mexico.

But it has never been applied to Israel, the country that over the past eight decades has received more U.S. aid, by far, than any other. That’s not because the Israel Defense Forces don’t commit serious abuses. “There are literally dozens of Israeli security force units that have committed gross violations of human rights” and should thus be ineligible for U.S. aid, a former State Department official, Charles Blaha, told ProPublica in May.

Mr. Blaha’s should know. From 2016 to 2023, he oversaw the office charged with enforcing the Leahy law. While a U.S. State Department spokesman in April claimed that Israel receives “no special treatment” under the Leahy law, Mr. Blaha says his own experience proved otherwise. When it came to every country except Israel, he has explained, career officials generally had the last word. In the case of Israel alone, he says, the decision rested with the State Department’s top political appointees.

Those appointees are failing to enforce U.S. law. This spring, ProPublica reported that an expert State Department panel had recommended that Secretary of State Antony Blinken cut off assistance to several units of the Israeli military and police after reviewing allegations that they had committed human rights abuses preceding the current Gaza war. In May, Mr. Blinken told Congress that Israel had adequately punished the members of units accused of serious abuses, and U.S. aid would thus keep flowing. (Because the department’s vetting process is not public, it’s unclear whether any of the units Mr. Blinken cleared were among those the panel flagged.)

Mr. Blinken has reportedly decided to even allow the United States to continue arming Israel’s Netzah Yehuda battalion. In 2022, members of the battalion dragged a 78-year-old Palestinian American man from his car near his home village in the West Bank, blindfolded, bound and gagged him, and left him near a construction site. He was unconscious when they came back and removed the bindings, about 40 minutes later. (Soldiers said they thought he was sleeping.) He was later pronounced dead from what an autopsy determined was a stress-induced heart attack. Seventeen months later, Israel’s military advocate general said the soldiers would face disciplinary measures but declined to press charges.

That’s typical. According to the Israeli human rights group Yesh Din, less than 1 percent of Palestinians’ complaints against Israeli soldiers between 2017 and 2021 led to prosecution. Even before Mr. Blinken’s reported decision to continue to aid this battalion because its violations had “been effectively remediated,” former Senator Leahy declared that America’s lack of enforcement toward Israel “makes a mockery of the law.”

It makes a mockery of the Biden administration itself, which often boasts of its commitment to the “rules-based order.” To ignore your own experts as well as global human rights groups and claim that not a single unit of the Israeli military is committing grave human rights violations — or that Israel is adequately punishing those who do — is absurd. It’s also lawless. And lawlessness is supposed to be what Ms. Harris is running against.

Some might argue that Israel can’t adhere to U.S. human rights laws and still fight its enemies. But if that’s the case, why does the United States apply the Leahy law to Ukraine, which is resisting a great-power invasion? For several years, the United States prohibited assistance to a battalion of Ukraine’s National Guard; the ban was lifted only this past June. The deep wisdom of the Leahy law is that violating human rights isn’t only morally wrong; it’s also strategically foolish. Those who believe killing Palestinian civilians makes Israel safer should remember that Hamas often recruits fighters from the families of the bereaved. As Ami Ayalon, a former head of Israel’s internal security agency, the Shin Bet, wrote in 2020, “If we continue to dish out humiliation and despair, the popularity of Hamas will grow.”

Granting Israel impunity may also encourage criminality at home. Last month, when Israeli military police tried to question reservists accused of sexual assault at the Sde Teiman army base, which has housed detainees from Gaza, several dozen protesters were joined by a far-right member of the Knesset who pushed his way through the army base’s gates. If Benjamin Netanyahu understood that units whose soldiers escape justice will lose their funding from the United States, he might more severely punish such thuggery.

Israel’s defenders often claim it is singled out for condemnation. But the beauty of the Leahy law is that it’s universal. When asked about Gaza, Kamala Harris doesn’t have to invent a new standard. She can just endorse the one enshrined in U.S. law. That won’t change U.S. policy overnight. But it will send a message, to officials such as Mr. Blinken and the officials Ms. Harris appoints if elected president, that the Israel exception to the Leahy law must end.

Ever since the declaration that “all men are created equal,” America’s leaders have been making statements of universal principle that they don’t apply universally. And ever since, other Americans have been fighting to make those words mean what they say. We’re in a moment like that again. The premise of the Leahy law is that all lives, including those of Palestinians, are equally precious. Kamala Harris can show, finally, that a major-party nominee for president agrees.