When the histories of his administration are written, it will be clear that Joe Biden held on to his callous disregard for Palestinians until the end of his presidency. How else to explain why Biden would refuse a final chance to stop Israel’s brutal war on Gaza and save Palestinian lives, when he has nothing to lose?

On Tuesday, the Biden administration quietly ignored its own deadline for Israel to increase the minuscule amount of humanitarian aid it allows to enter Gaza. The US secretary of state, Antony Blinken, and defense secretary, Lloyd Austin, imposed the 30-day deadline in a letter sent to Israeli officials on 13 October, which warned that they must take “concrete measures” to ensure that Palestinian civilians in northern Gaza have access to food, medicine and other necessities. The administration said it could suspend US military support to Israel if conditions did not improve. Despite the US ultimatum, the amount of aid reaching the besieged territory in October had dropped to its lowest level in 11 months.

As the deadline passed, the Biden administration did what it has done for more than a year: it caved and continued sending weapons to the government of the Israeli prime minister, Benjamin Netanyahu, despite the devastation and famine Israel has inflicted on Gaza. And Washington sheepishly told the world that it would not impose any consequences on Israel, even though the US is legally bound to stop arming an ally that blocks humanitarian aid in a conflict zone.

It’s the latest in a long series of decisions by Biden over the past 13 months that show his disdain for Palestinian lives. But his lack of action this week is especially egregious because Biden is politically unrestrained: the presidential election is over, and Donald Trump won. Biden can do whatever he wants without incurring a political cost. He doesn’t even have to worry about a transition to his fellow Democrat and vice-president, Kamala Harris. If there was ever a time for Biden to use his considerable power to save Palestinians, this was it. Yet he squandered this final opportunity to make the right and moral choice – and help end the Gaza war before leaving office.

Biden’s decision to keep supplying weapons to Israel reinforces his legacy as the primary enabler of the slaughter in Gaza, and Netanyahu’s campaign to expand the war into Lebanon. While Biden and his allies have done a lot of hand-wringing about Trump’s disregard for the rule of law, the Biden administration failed to uphold US law and its own policies – and it has undermined US credibility around the world even before Trump takes office once again.

Biden has been fully complicit in Israel’s destruction of Gaza, in which more than 43,000 Palestinians have been killed, although the true figure is probably much higher. One estimate published by researchers in the Lancet, a medical journal, found that the death toll could eventually reach 186,000. That accounts for “indirect casualties” of war, such as widespread hunger, a cholera epidemic, unsanitary conditions and the destruction of Gaza’s health system.

Following a relentless Israeli military assault that started after the Hamas attacks of 7 October 2023, nearly all of Gaza’s 2.1 million people have been displaced at least once, and are now living in makeshift tents or in the ruins of bombed-out buildings. Last week, a UN-affiliated group of experts warned that famine is imminent, or may already be unfolding, in northern Gaza – and that the enclave’s entire population faces acute food insecurity, which is one step below a full-blown famine.

Days after Biden decided to continue arming Israel into the twilight of his presidency, Human Rights Watch (HRW) released a devastating 154-page report that contradicted most US and Israeli assurances that Israel is not violating international law. The report, issued on Thursday, concluded: “Israeli authorities have caused the massive, deliberate forced displacement of Palestinian civilians in Gaza since October 2023 and are responsible for war crimes and crimes against humanity.” HRW urged western governments to impose sanctions and suspend their arms shipments to Israel.

The US has provided Israel with nearly $18bn in weapons and other military assistance since October 2023, according to a report released last month by Brown University. Washington spent another $4.8bn on its own military activities in the Middle East due to the conflict. Overall, the Biden administration spent at least $22.7bn in US taxpayer funds to enable Netanyahu and his government to prolong the Gaza war.

But the US administration did not have to become so deeply complicit in Israel’s war crimes. Biden and his aides had the leverage, policy tools and legal mechanisms to restrain Israel, end the conflict, and save thousands of Palestinian lives. For months, Biden, along with his secretary of state, squandered any influence they could have exerted over Netanyahu by refusing to enforce US law and their own administration’s policies on weapons transfers.

In February, as Biden faced pressure from a handful of Democrats in Congress critical of his unwavering support for Israel, he issued a new national security memo which required the state department to certify that recipients of US weapons would allow the delivery of humanitarian aid during active conflicts and abide by international law. Biden’s memo did not set new policies for arms transfers to foreign countries, but instead used provisions of existing US laws, especially under the 1961 Foreign Assistance Act.

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Washington can suspend shipments if it suspects that a foreign military will use US weapons to carry out violations of international law, or to countries that block the delivery of humanitarian aid – as Israel has done throughout its war in Gaza. By May, the state department sent a 46-page report to Congress full of bureaucratic double-speak to justify Biden’s decision to flout US and international laws to protect Netanyahu.

Long before the administration’s report, the UN and human rights groups had amply documented that Israel was using starvation as a weapon of war – a violation of international law – and deliberately blocking food and other supplies from entering Gaza.

Yet the report avoided concluding that the Israeli military had obstructed humanitarian aid, or violated international law while using US weapons. Such findings would have forced Biden to suspend most weapons shipments to Israel under the policies outlined in his own national security memo. But instead of upholding US law and using the suspension of military support to force Netanyahu to accept a ceasefire, Biden sat by and enabled Israel to kill thousands of Palestinians since May.

Back then, Biden was still running for re-election and could have feared political repercussions for breaking with Netanyahu. But this week, the US president was as free from politics as he’s ever been in his entire career. He simply decided that Palestinians don’t matter – and sealed his legacy as the enabler of Israel’s war crimes.

• Mohamad Bazzi is director of the Hagop Kevorkian center for Near Eastern studies, and a journalism professor at New York University