In the fall of 2016, the Obama administration sealed a major military agreement with Israel that committed the United States to giving the country $38 billion in arms over 10 years.

“The continued supply of the world’s most advanced weapons technology will ensure that Israel has the ability to defend itself from all manner of threats,” President Barack Obama said.

At the time, the agreement was uncontroversial. It was a period of relative calm for Israel, and few officials in Washington expressed concern about how the American arms might one day be used.

Now that military aid package, which guarantees Israel $3.3 billion per year to buy weapons, along with another $500 million annually for missile defense, has become a flashpoint for the Biden administration. A vocal minority of lawmakers in Congress backed by liberal activists are demanding that President Biden restrict or even halt arms shipments to Israel because of its military campaign in Gaza.

Mr. Biden has been sharply critical of what he on one occasion called “indiscriminate bombing” in Israel’s war campaign, but he has resisted placing limits on U.S. military aid.

The United States and Israel have had tight military relations for decades, stretching across multiple Democratic and Republican administrations. Israel has purchased much of its critical equipment from the United States, including fighter jets, helicopters, air defense missiles, and both unguided and guided bombs, which have been dropped in Gaza. Legislation mandates that the U.S. government help Israel maintain force superiority — or its “qualitative military edge” — over other Middle Eastern nations.