For Biden, the commitment to conditioning U.S. military aid for Israel and other allies and strategic partners will help him shore up support among center-left Senate Democrats for his proposed $95-billion supplemental assistance package, which is aimed primarily at military aid for Ukraine in its war with Russia and for Israel in its war against Hamas in Gaza.

Democratic senators on Friday called Biden’s directive — meant to bring breadth, oversight, deadlines and teeth to efforts to ensure foreign governments don’t use U.S. military aid against civilians — historic.

“This is a sea-change in terms of how you approach U.S. military aid and its impact on civilians,” Sen. Elizabeth Warren of Massachusetts said. She spoke at a Capitol news conference with other Democrats who’d negotiated with the White House for two months on the matter, in an effort led by Sen. Chris Van Hollen of Maryland.

Human rights advocates said the challenge for the new directive would be the same faced by all previous efforts to withhold U.S. weapons and funding from human rights abusers — whether administrations will enforce the human rights conditions for strategically important allies and partners.

“The issue was never knowledge” of U.S. military aid being used in violation of international law “so much as enforcement,” said Kenneth Roth, a former head of Human Rights Watch and a visiting professor at Princeton School of Public and International Affairs.

The new order comes in what’s officially known as a presidential memorandum. Those have the force of law, although succeeding presidents can overturn them.

Biden’s order has immediate effect. It gives Secretary of State Antony J. Blinken 45 days to obtain “credible and reliable written assurances” from foreign recipients of U.S. military aid that are in active conflicts, which includes Israel and Ukraine, that they are using U.S. military assistance in compliance with international humanitarian law and human rights law and other standards.

Foreign governments that fail to provide those assurances on time would have their military aid paused. Administrations also have the option of suspending U.S. military assistance if they deem a foreign government isn’t complying with humanitarian law and protections while claiming it is.

Other requirements include regular reports from the administration on compliance going forward. That includes countries not actively fighting a war.

The supply of air defense systems and some other defensive gear is exempted. While supporters say the stringent language of the order will limit the ability of presidential administrations to evade the spirit of the measure, the order does allow administrations to waive the requirements in “rare and extraordinary circumstances.”

The Biden administration has frustrated some Senate Democrats during Israel’s war in Gaza by declaring a national security emergency to rush military aid to Israel, skirting the usual process of congressional notification.

The administration also has quietly lobbied against moves by independent Sen. Bernie Sanders and others to attach conditions to military aid to Israel in the supplemental legislation, with the idea of pressuring Israel to do more to spare Palestinian civilians.

Nearly 28,000 Palestinians, two-thirds of them women and children, have been killed since Israel launched its military campaign in Gaza, according to the Palestinian Health Ministry. That followed the Oct. 7 attacks by Hamas that killed about 1,200 people in Israel.

Israeli Prime Minister Benjamin Netanyahu’s government has not appeared to have substantially backed away from daily airstrikes claiming civilian lives despite the pressure from the United States, its most important ally and military supporter. The U.S. is also frustrated at Israel’s restrictions on humanitarian aid deliveries into Gaza. Biden this week leveled some of his strongest criticism of Israel’s conduct of the war, calling it “over the top.”

White House Press Secretary Karine Jean-Pierre underscored Friday that the administration is “not imposing new standards for military aid” with the memorandum. She said it was done in the interest of improving transparency.

She added that Israeli officials were briefed on the memorandum before its release.

“They reiterated their willingness to provide these types of assurances,” Jean-Pierre said.

The U.S. already has laws — including the Foreign Assistance Act and the Leahy Law — meant to bar security assistance to governments that are serial human rights abusers. Those “are honored in the breach,” said Roth, the human rights expert.

“If the administration is so indifferent to existing law, it’s not clear what difference a new set of reports will make,” Roth said.

The Democratic senators said Friday they would continue working to strengthen the new system laid out in the order.

That includes seeking funding for the additional government oversight and codifying it into legislation so it’s harder for future presidents to ignore.

“This is a very big deal,” Van Hollen said. “And it will give President Biden and the United States more tools and more leverage … to ensure that U.S. military assistance complies with American values and American” standards.

Seung Min Kim contributed to this report.