If there is one foreign policy objective to which Donald Trump is unalterably committed, it is bringing the Iranian theocracy to its knees -- or at least thwarting its nuclear ambitions.
This is the reason the President, against the advice of all of America's leading allies, has clamped new and potentially existential sanctions on Iran for violating a treaty that the world believes it has respected to the letter if not the spirit.
But if he is to achieve this demolition of the Iranian system, it is becoming quite clear that Trump will have to accept Mohammed bin Salman, widely accused as the mastermind behind the killing of Washington Post columnist Jamal Khashoggi, as the effective ruler of Saudi Arabia with all that entails for a generation to come. And that entails quite a lot. MBS denies he ordered the killing.
The resolution of a host of problems in the Middle East -- especially Iran, Qatar and the endless war in Yemen -- revolves around Western, and especially American, acceptance of Saudi Arabia's deeply felt need for security.
The road to this security runs directly through the vicious, uncompromising hegemony of Mohammad bin Salman. That's the conclusion of Ali Shihabi, founder of the Washington-based Arabia Foundation, who, according to journalist and scholar Thomas Lippman, often unofficially speaks authoritatively for Saudi Arabia's ruling al-Saud family.
Shihabi believes that all too many of the recent moves by MBS, as he is known inside and outside the kingdom, have been deeply flawed.
But he also observes that "the crown prince has never pretended to be a political reformer," which is not entirely true.
Indeed, his pretensions at being just a such a reformer—allowing women to drive, opening cinemas—are what particularly endeared him to a broad, even bipartisan swath of Washington.
But Shihabi, in an effort to clarify, observes correctly: "He is the Crown Prince of an absolute monarchy who understands that economic and social transformation is essential to safeguarding the future of his country and who believes that such change in a deeply polarized country like Saudi Arabia can only come from the top."
In short, Shahibi concedes, in his extraordinary document, MBS "is not a Jeffersonian democrat," but has the Saudis' ultimate security at heart.
And apparently at any cost. Which helps to explain where, and how, Donald Trump comes in. The cost will undoubtedly be a heavy one -- especially after Monday, as Trump snaps back sanctions against Iran that had been lifted after that nation signed the agreement sharply restricting its nuclear ambitions.
To make these stick, Trump needed some other ally. Along came Saudi Arabia -- and especially MBS.
The price of MBS' support has turned out to to be a high one. There was free rein for the Crown Prince to do as he liked whenever he desired.
Not everyone, of course agreed with this assessment.
Then there was bin Salman's blockade of Qatar, home to the powerful Al Jazeera news channel and ruled by a monarch who's been ill-inclined to toe the Saudi line.
Finally, the brutal war in Yemen, which Saudi Arabia pursues in the face of virtually every international plea.
American aircraft continue the aerial refueling of Saudi-led bombers, who have left tens of thousands of civilians, even children, dead and millions on the verge of starvation—one of the world's most acute humanitarian emergencies.
But it is Iran that holds the gravest potential as a long-term, irreversible crisis. Should Iran see the latest turn of the screw by the Trump administration and his Saudi backers as an existential threat, scrap the nuclear accord and return full-tilt to building a nuclear arsenal, there will be no putting that genie back in the bottle.
The principal problem is that all sides at this point just can't seem to be able to get out of their own way.
Saudi Arabia has simply ignored even the Trump administration's call for a ceasefire in Yemen.
At the same time, Iranian agents were accused of an assassination plot against a regime foe in Denmark, outraging the European community, which has bitterly opposed Trump's renewal of American sanctions on Iran.
What the world really needs is for someone to become the adult in the room. Ideally, that person should be Donald Trump.
Yet somehow, when the President gets on the phone to talk with the aging, but still supremely powerful King Salman, Trump seems to lose all sense of reason.
The conversations are invariably wonderful and productive. "Just spoke to the King of Saudi Arabia who denies any knowledge of whatever may have happened 'to our Saudi Arabian citizen,'" Trump tweeted last month at the height of the Khashoggi crisis.
Of course, it's possible that someone else is sitting on the other end of these calls along with the King -- perhaps his son, who is utterly out of control. A White House official said they do not discuss arrangements for top-level phone calls.
It's now past the time when we need to know with certainty who's minding the store. It's too late and the stakes are too high for us to plunge blindly into the abyss.