PARIS—Donald Trump decided to endorse the leadership of an alleged Saudi murderer on Tuesday.

Speaking of accusations by the CIA and others that Crown Prince Mohammed bin Salman ordered the assassination of journalist Jamal Khashoggi, the president of the United States reverted to his usual fallback position: the truth is unknowable.

“It could very well be that the Crown Prince had knowledge of this tragic event—maybe he did and maybe he didn’t!” Trump said in a statement that read as if he'd dictated it off the top of his head and refused to allow corrections.

“We may never know all of the facts surrounding the murder of Mr. Jamal Khashoggi,” Trump said. “In any case, our relationship is with the Kingdom of Saudi Arabia.”

This is pitiful, and untrue.

The United States does have a longstanding, complicated relationship with the Saudis. But Trump has reduced all international relations to monetary transactions and the personalities of leaders he thinks he can trust. In the Middle East, that’s meant the Trump administration has only ever had one policy, and its name was Crown Prince Mohammed bin Salman.

MBS, as he’s come to be known, promised the players in the Trump-Kushner regime all they could ever dream of: vast amounts of money, victory as warriors, honor as peacemakers. He’d put the whole world in their hands, like that creepy glowing globe they fondled on their debut trip abroad to his hometown in 2017.

Now all that is in doubt. The man who promised Trump everything promises to be a liability for at least as long as Trump is in power, and then some: a homicidal millennial headed to his decrepit father’s throne and only 33 years old in a family where, for better or worse, many men live into their eighties.

When the CIA determined “with high confidence” that Mohammed bin Salman ordered the slaughter of journalist Jamal Khashoggi—whose body allegedly was chopped to bits on Oct. 2 in the the Saudi consulate in Istanbul—it also made another determination. According to a report on the agency’s conclusions in The Washington Post, CIA analysts believe that despite the global uproar about the murder, MBS “is likely to survive” and it is “taken for granted” he will be king.

If that’s the case, the question is not what happens if MBS goes, as some pundits in Washington are asking, but what happens when he stays?

LET‘S LOOK BACK FOR A MOMENT at a snowy day in March 2017, when German Chancellor Angela Merkel had to postpone a lunch at the White House and MBS stepped in after morning meetings, sealing his bond with Trump and the several amateur statesmen of the new administration.

One of the deputy national security advisers, Derek Harvey, had been promoting the notion that Iran was the supreme enemy and Saudi Arabia was the solution, according to Bob Woodward’s book Fear. Trump echoed that view in his statement Tuesday. But the senior professionals of the time — Chief of Staff H.R. McMaster, Secretary of Defense James Mattis, Secretary of State Rex Tillerson (who had dealt with the Saudis all too many times on oil deals as CEO of Exxon)—thought this was likely to be a disappointing exercise.

“ When MBS offered himself to Kushner as his guy in the Saudi kingdom, that was ‘like meeting someone nice at your first day of boarding school.’ ” — Michael Wolff in “Fire and Fury”

“The Saudis always talk a big game,” Tillerson said, according to Woodward. ”You go through the dance with them on the negotiations. When it comes time to putting the signature on the page, you can’t get there.”

Never mind. In the spring of 2017, Trump was desperate for a “win.” His big promises during the campaign about health care, infrastructure, and true tax reform were not materializing. Meanwhile, MBS had been courting Trump son-in-law and senior adviser Jared Kushner, and on that snowy day MBS met Trump himself.

“The two large men, the older Trump and much younger MBS—both charmers, flatterers, and country club jokers, each in his way—grandly hit it off,” Michael Wolff wrote in Fire and Fury, which aptly described the Trump regime’s reality-show approach to the Middle East. The idea in the White House that anything previous administrations did was stupid was founded in fact on abysmal ignorance.

“There was something curiously aligned between the Trump family and MBS,” Wolff wrote. “Like the entire Saudi leadership, MBS had, practically speaking, no education.” Serendipitously and sadly, that put Trump and MBS on a more or less equal footing. “Knowing little made them oddly comfortable with each other. When MBS offered himself to Kushner as his guy in the Saudi kingdom, that was ‘like meeting someone nice at your first day of boarding school,’” wrote Wolff, citing an anonymous Kushner friend.

MBS PROMISED IN EFFECT to be the one-stop shop for Middle East solutions, and he must have sounded pretty convincing to people who really had no clue about the region. He was going to deliver the Palestinians for the peace process and recognize Israel, pulling the United Arab Emirates and others along with him. He was going to shore up the wall against Iranian aggression, and take the war home to Tehran. He was going to manage oil prices in a way that benefited the United States, and especially the Trump regime. And that Yemen thing? That wildly misconceived war? No problem. Wrap that up in a matter of months if not of weeks.

In the meantime, why not make the Trumps’ first presidential trip abroad to Riyadh, where the Trumps and the Saudis could promote all these great ideas? Plus, the Saudis would re-commit, at least verbally, to all those arms deals Obama signed off on. $110 billion. Trump could talk about “jobs jobs jobs.” Oh, and Saudi Arabia would privatize Aramco. Money, for nothing.

None of those promises panned out. Tillerson had been right.

Then comes the Khashoggi affair and everything turns to shit. The guy behind the counter at that the Saudi One-Stop Mideast Policy Drive-Thru turns out to be a psychopath.

“ The man who promised Trump big wins in the Middle East is making him look like a loser. Or an idiot. Or both. ”

BUT ... IF YOU ARE TRUMP, what are you gonna do? We saw that on Tuesday. He clearly thinks if he can just whitewash MBS enough, while playing up Iran as the root of all evil, people might turn the page and assume, to paraphrase Franklin D. Roosevelt talking about a banana republic dictator, “He’s a psychopath, but he’s our psychopath.”

Unfortunately for Trump, that doesn’t seem to be working, and the man who promised him big wins in the Middle East is making him look like a loser. Or an idiot. Or both.

"Trump’s thinking on Saudi is magical," says Aaron David Miller at The Wilson Center. "So far he has accommodated a guy who has been a source of instability not stability."

Bruce Riedel at Brookings agrees. "The most likely near term scenario is MBS stays but is crippled and can’t deliver. He will be a pariah in the West."

Of course we know Trump is a sucker for authoritarian assassins: Vladimir Putin, Kim Jong Un, Rodrigo Duterte, to name a few. But MBS now appears in a class by himself, not for the quantity of his killing (the foolish Yemen war aside) but for the quality of his ineptitude. Trump has scrambled to cover for the crown prince in the Khashoggi affair, wishing it would all just go away, but he continues to be confronted by the growing realization that this murderous Saudi who promised him so much is not only reckless, he’s inept.

Barbara Bodine, a former ambassador with years of experience on the Arabian Peninsula, notes, “MBS may slide through for the rest of this administration, but he will be permanently tainted. Every action or non-action will be seen through the filter of Jamal Khashoggi. Every act will be judged on ruthless to reckless to feckless. And, as he is increasingly unable to deliver—no victory in Yemen, no collapse of Qatar [which MBS tried to crush], and, if oil prices drop, no welfare state and no grand projects, he could become The Hollow Prince.”

Trump, defending him, exposes a hollow presidency.