The Trump administration’s decision to push Saudi Arabia to bring the war in Yemen to an end and lift its blockade of Qatar is overdue. These were costly misadventures that should have been halted already. Now that the killing of Jamal Khashoggi has weakened the hand of Crown Prince Mohammed bin Salman, the architect of both policies, there’s a better chance that outside pressure will succeed.

The war in Yemen has been a humanitarian calamity. Now in its fourth year, it has killed at least 10,000, and put 14 million, nearly half the population, on the brink of starvation. It has aggravated the global refugee crisis, divided the Arab world and hobbled the military forces of the Saudi-led coalition.

The original objective — to defeat the Houthis, a rebel militia loosely backed by Iran that had ejected a pro-Saudi government from Sanaa — is no closer to being realized. The Houthis retain control of the Yemeni capital, and their relationship with Iran has, if anything, deepened. The Trump administration needs the Arab world to unite in opposition to Iran, and the war has made that harder.

The U.S. provides arms and intelligence support to the Arab coalition, so it has leverage in imposing the 30-day deadline announced by Defense Secretary Jim Mattis for cease-fire talks. It should recruit the Sultan of Oman, who has kept his country out of the fighting and who maintains contact with both Iran and the Houthis, to persuade the rebels to negotiate. And Washington should lead a global relief effort to stave off starvation and disease among the Yemenis.

Many of the countries in the Saudi coalition also joined in the blockading of Qatar last year, accusing it of being too close to Iran. The isolation has had little effect on Qatar’s economy — and again, it has led to closer relations between the emirate and Iran. Qatar hosts an enormous U.S. air base and is an important ally. The Trump administration has been quietly urging Prince Mohammed to end his feud with Emir Tamim bin Hamad Al Thani. The White House ought now to speak more forcefully.

The U.S. and Saudi Arabia share the larger goal of keeping Iran in check. Next week, the U.S. will impose crippling new sanctions — the clearest expression so far of the Trump administration’s determination to constrain Iran’s rulers. The crown prince can prove his own commitment to that cause by starting to undo two of his biggest mistakes.