And I believe that the roots of 9/11 came from two terrible bargains. One was that bargain between the Saudi ruling family and the kingdom’s religious establishment, where each blessed the other. The other was America’s cynical bargain with the Saudis, which went like this: “Guys, just keep your oil pumps open, your prices low and don’t bother the Israelis too much, and you can do whatever you want out back — preach whatever hate you want in your mosques, print whatever conspiracy theories you want in your papers and treat your women however you want.”

On 9/11 we got hit with the distilled essence of everything that was going on out back. Which is why this column, since 9/11, had been highly critical of Saudi leaders for not reforming their version of Islam, something that would require economic and social modernization as well. They would arrest religious extremists, but Saudi leaders almost never engaged them in a public war of ideas.

And so what most caught my eye about M.B.S. and made me most hopeful was his tentative willingness to engage in a war of ideas with his religious hard-liners, declaring publicly: “Do not write that we are ‘reinterpreting’ Islam — we are ‘restoring’ Islam to its origins.” He argued publicly that Islam in its origins was tolerant of other faiths and empowering of women and open to new ideas.

He seemed to be aiming to replace Saudi fundamentalist Islam, and its clerics, as the primary source of his regime’s legitimacy with a more secular Saudi nationalism — one, to be sure, that had a strong anti-Iran and anti-Qatar tenor.

Hey, maybe it was all just a fake to cover for a power grab and win Western support. But a lot of young Saudis I spoke to thought it was real and wanted more of it. On this question of Saudi Arabia’s most toxic export that had affected America and the whole world — jihadi Islamism — M.B.S. was doing and saying stuff that had real promise.

As veteran U.S. Middle East negotiator Dennis Ross recently pointed out in an essay in The Washington Post: “M.B.S.’s appointment of Muhammad al-Issa as the head of the World Muslim League has sent a powerful new message of tolerance and rejection of radical Islamist teachings. His visit to the U.S. Holocaust Museum, his commitment to interfaith dialogue and his calls for peace mark a significant departure from his predecessors.”

But now M.B.S.’s government also has Jamal’s blood on its hands. Should we all overlook that as President Trump is doing? We must not, and, in fact, we cannot.