His critics would say that Mr. Trump is now similarly emboldening a reckless Saudi regime.

This is a false analogy. The Saudis are not the moral equivalents of Iranians and the Russians. The kingdom has sheltered comfortably for over 75 years under the American security umbrella, which the United States happily extended not least because the Saudis and their oil have played a pivotal role in American economic strategies. Mr. Trump’s statement acknowledged that the Saudis are assisting him with stabilizing global oil prices as he seeks to quash Iranian oil sales.

Whatever Prince Mohammed’s faults may be, he actively supports the American regional order that the Iranians openly seek to destroy.

Mr. Trump’s critics are asking us to believe that the priority for stabilizing the Middle East today is distancing the United States from one of its oldest allies and instead working to achieve a balance of power between Riyadh and Tehran. The Saudis, they claim, need us far more than we need them.

This is a dangerous assumption that is not born out by experience. In recent years all of America’s allies, from Mr. Sisi in Egypt to Recep Tayyip Erdogan in Turkey to Benjamin Netanyahu in Israel, have begun spending as much time in Moscow as in Washington. Why would we think the Saudis might not also seek protection from Russia if they are shunned by America?

Instead of standing with the Saudis, Mr. Trump’s critics call for, as Senator Lindsey Graham recently did, sanctions that would persuade King Salman to appoint a new crown prince. But King Salman is not the de facto ruler of Saudi Arabia; Prince Mohammed is. A policy that seeks to change the king’s mind is based on a delusion that is far more deranged than anything in Mr. Trump’s statement.

Let’s imagine Mr. Trump’s critics get their wish. A replacement crown prince who rose to power under pressure of sanctions would be severely weakened, if not entirely illegitimate. This would serve only to validate Al Qaeda’s anti-Saudi ideology, which depicts the royal family as American stooges. Would a compromised crown prince be a more reliable partner for the United States in stabilizing the Middle East?

In all likelihood, sanctions would simply embitter Prince Mohammed, who would respond by tacking toward Russia and China. The United States could console itself by celebrating its staunch commitment to principle, but its influence would diminish considerably.