TWO WEEKS ago, the Trump administration took a first step toward reining in the reckless Saudi regime under Crown Prince Mohammed bin Salman, calling for a cease-fire in the war Saudi Arabia has been waging in Yemen — a military failure that has created the world’s worst humanitarian crisis. The Saudi response: a new offensive with its allies against the port of Hodeida, through which flows 70 percent of the food and medicine for Yemen’s 28 million people — half of whom are on the brink of starvation.

An attack on the city was suspended earlier this year under pressure from the United States and the United Nations. Now Saudi planes are again bombing, probably using U.S.-supplied munitions; according to Amnesty International, there were explosions Sunday close to Hodeida’s most important hospital. On Friday, the Pentagon took another step, ending refueling operations for Saudi planes fighting in Yemen. But that also did not stop the offensive. The BBC said street fighting was reported to be continuing Monday.

Mohammed bin Salman launched the Yemen intervention in 2015, not long after he took over the Saudi defense ministry. It was supposed to lead to a quick rout of Houthi rebels who had driven Yemen’s government out of the capital, Sanaa. Instead it has become a quagmire in which more than 16,000 civilians have been killed or injured, mostly in Saudi airstrikes that have hit schools, mosques, markets, weddings, funerals and, in August, a bus full of children. Unchastened by that record, the crown prince has since pursued a series of further misadventures, culminating with the murder of journalist Jamal Khashoggi on Oct. 2.

Mohammed bin Salman’s apologists whisper that he has been chastened by the backlash against the Khashoggi murder; that his wings have been clipped; that his militant advisers have been replaced by older and wiser heads. If so, there is no evidence of it in Yemen. On the contrary, the Riyadh regime is all but spitting in the face of one of its last defenders — the Trump administration, which has been trying to protect the crown prince. On Sunday, Secretary of State Mike Pompeo called Mohammed bin Salman and “reiterated the United States’ calls for a cessation of hostilities,” according to the State Department. But at the same time, Mr. Pompeo continues to pretend that Mohammed bin Salman can “hold all of those involved in the [Khashoggi] killing” responsible — even though the crown prince himself is a prime suspect.

The United States is rightly supporting a U.N. effort to launch peace negotiations on Yemen by the end of the year. But it has become clear that the only way to force a cease-fire and rescue the millions facing famine and cholera is to end all military support for both Saudi forces and those of its United Arab Emirates allies. There should be no more sales or deliveries of munitions and spare parts; all U.S. intelligence and technical support should be frozen. If the Trump administration will not get tough on the crown prince, on whom it has unwisely pinned much of its Middle East strategy, Congress should act in its place.