Yemenis carry a casket on Aug. 13 as they take part in a mass funeral in the northern Yemeni city of Saada. (STRINGER/AFP/Getty Images)

THE MURDER of Jamal Khashoggi should spark a long-overdue recalibration of U.S. relations with Saudi Arabia and its reckless de facto leader, Mohammed bin Salman. In the past several years the crown prince has launched a series of foolhardy foreign policy initiatives that have damaged U.S. interests, including his rupturing of relations with Qatar and Canada and the kidnapping of the pro-American Lebanese prime minister. But the best place to start the U.S. readjustment is where Mohammed bin Salman himself began: with the disastrous war in Yemen.

Saudi Arabia and its allies plowed into Yemen in 2015, after a northern rebel group, the Houthis, captured the capital and ousted a Saudi-backed government. Saudi officials confidently promised to make quick work of the Houthis. After more than three years of fighting, including a U.S.-backed bombing campaign that has killed thousands of civilians, the Saudi coalition, which includes the United Arab Emirates, has come nowhere near to achieving that objective.

Instead it has triggered what the United Nations describes as the world’s worst humanitarian crisis while committing atrocities that a U.N. investigative panel said were probable war crimes. Eight million Yemenis are in danger of starvation, and more than 1 million have contracted cholera — the worst such epidemic in modern history. Yet UAE forces, ignoring U.N. appeals, are besieging the port through which 70 percent of food and medicine supplies are imported. The Saudis keep dropping U.S.-supplied bombs on civilian targets: On Aug. 9, one struck a school bus, killing at least 51 people, including 40 children.

The Saudis say they are countering Iran, which backs the Houthis. But the Houthis are an indigenous group with legitimate grievances, and the war has only enhanced Iranian influence. As has been obvious for some time, the only solution is a negotiated settlement. But the Saudis have done their best to sabotage a U.N.-led peace process. Talks planned for Geneva in September failed when Saudi leaders would not grant safe travel guarantees to Houthi leaders.

Congressional concern about this strategic and humanitarian disaster has been mounting. In March, the Senate nearly approved a resolution cutting off U.S. aid, including refueling and targeting assistance. In August, Congress approved a defense bill that required the administration to certify that the Saudis were taking steps to minimize humanitarian casualties and facilitate humanitarian deliveries. Against overwhelming evidence to the contrary and the advice of State Department experts, the administration issued the certification last month.

Mr. Khashoggi’s death should resurface the issue, as senators from both parties are proposing. Sen. Robert Menendez (D-N.J.) has been holding up a Saudi request to purchase precision-guided munition kits for its bombs; that blockage should be formalized, along with a ban on all other aid to the Yemen war.

Iran hawks will howl that the prohibition will work to Tehran’s advantage. But the Trump administration’s unquestioning support for what amounts to a sectarian crusade by Sunni Saudi Arabia against Shiite Iran needs an adjustment, too. Iran’s attempt to establish itself as a regional hegemon should be resisted. But that can be achieved without buying into Mohammed bin Salman’s own imperial — and unachievable — ambitions.