Trump has given Mohammed bin Salman and his purges  his full endorsement tonight:
I have great confidence in King Salman and the Crown Prince of Saudi Arabia, they know exactly what they are doing….
— Donald J. Trump (@realDonaldTrump) November 6, 2017 
Trump’s embrace of the Saudis has been one of the greatest blunders of his presidency to date, and today he has reaffirmed that he has profoundly bad judgment when it comes to this relationship. There is no reason to have confidence in Salman and his son after the last two and a half years, and there is certainly nothing to support the claim that they know what they are doing. The war on Yemen has become a quagmire for the Saudis and their allies and a catastrophe for the people of Yemen. Trump supports it. The campaign against Qatar has been a useless and ill-advised misadventure that is also hurting members of the Saudi-led bloc. Trump has been an enthusiastic cheerleader. The crown prince is carrying out a massive purge that will drive away foreign investment in the short term and destabilize the kingdom. Once again, Trump is only too happy to approve of anything the Saudi government does, no matter how dangerous or despicable it may be.
Considering his claims to represent American nationalists, it is laughable that Trump is one of the most obsequious sycophants of the Saudi government in the world. Nothing could be less populist or less “Jacksonian” than sucking up to a foreign despotic government in this fashion. As a candidate, Trump criticized the Saudis for taking advantage of the U.S., but since taking office he has been eager to curry favor with them no matter the cost. Thanks to their flattery earlier this year in Riyadh and Trump’s own Iran obsession, he has proven to be the easiest mark the Saudis could have hoped to find. The U.S. and the entire region stand to lose a great deal from continuing to indulge one of our worst clients, and Trump will be remembered for his shameless embrace of one of the world’s most awful regimes.