No doubt President Trump was unaware of the significance of the date he chose to salute “my friend MBS.”

No doubt Trump had no idea that it was the year-and-a-half-anniversary of the murder of Jamal Khashoggi.

But, yes, Trump’s tweet came 18 months to the day after his “friend MBS” — Saudi Crown Prince Mohammed bin Salman — had a hit squad murder Khashoggi inside the Saudi Consulate in Istanbul. A hit squad that included forensic doctor Salah Mohammed Tubaigy, who brought his bone saw with him from Riyadh.

You probably remember the outlines of the story. A respected Saudi journalist living in Virginia and writing columns for The Post, Khashoggi had visited the consulate the previous week seeking paperwork so he could marry his Turkish fiancee, Hatice Cengiz. He had been told, no problem, come back the following Tuesday — Oct. 2, 2018.

He returned around 1 p.m., asked Cengiz to wait out front, told her he would return shortly.

She waited — an hour, two, 10. After midnight, he still had not reappeared.

By the next day, friends and colleagues were alarmed, though few understood the true depravity of the Saudi regime, and Saudi lies postponed understanding.

“I assure you that the reports that suggest that Jamal Khashoggi went missing in the Consulate in Istanbul or that the Kingdom’s authorities have detained him or killed him are absolutely false, and baseless,” Prince Khalid bin Salman — the Saudi ambassador to the United States and MBS’s little brother — was still saying on Oct. 8.

But Turkish authorities knew what had happened. They knew the bone-saw doctor had expressed the hope, just before Khashoggi entered the consulate, that it would “be easy. Joints will be separated. It is not a problem. The body is heavy. First time I cut on the ground. If we take plastic bags and cut it into pieces, it will be finished. We will wrap each of them.”

The bone-saw doctor was speaking to Maher Abdulaziz Mutreb, a Saudi intelligence officer who also had been dispatched from Riyadh. As Tubaigy finished his explanation, Mutreb asked whether “the sacrificial animal” had arrived.

U.S. intelligence officials concluded that the murder could not have taken place without the crown prince’s authorization. An investigation by U.N. special rapporteur Agnes Callamard called the murder and dismemberment “an extrajudicial killing for which the State of the Kingdom of Saudi Arabia is responsible.”

For a time, the Trump administration pretended to seek information about the killing. The truth would come out, Trump said. Secretary of State Mike Pompeo pressed the crown prince at least to move aside his chief henchman, Saud al-Qahtani.

But any pretense is long gone. Qahtani remains influential. The administration has illegally ignored congressional mandates to furnish information on the killing and impose sanctions.

And now, as though to mark a year and a half of Saudi nose-thumbing, Trump is prostrating himself again. The reason: As a pandemic imperils the American economy, the Saudis have threatened to devastate the U.S. oil industry further by flooding the market with cheap oil.

“Just spoke to my friend MBS (Crown Prince) of Saudi Arabia, who spoke with President Putin of Russia, & I expect & hope that they will be cutting back approximately 10 Million Barrels, and maybe substantially more which, if it happens, will be GREAT for the oil & gas industry!” Trump tweeted on Thursday.

This quickly turned out to be — surprise, surprise — false, at least in its details; the Kremlin denied that Putin and Mohammed bin Salman had spoken.

It may well prove false in the big picture, too. There is no sign of an agreement between Russia and Saudi Arabia. The Wall Street Journal reported Friday that those two countries wouldn’t throttle back unless U.S. producers also reduced output, which could, among other complications, put them on the wrong side of U.S. antitrust law.

All of which would fit the pattern of Trump’s infatuation with the Saudi royal family, which from the start has played him for a fool. Trump made Saudi Arabia his first overseas destination, and the king threw a dazzling reception and promised, Trump claimed, to buy hundreds of billions of dollars worth of U.S. weaponry.

In the years since, few of those sales have materialized. Meanwhile, the administration has sent thousands of U.S. troops to help defend the kingdom, even as Trump claims to be disentangling from the Middle East. The United States has signed on to or acquiesced in every reckless MBS action — a feud with neighboring Qatar, a disastrous war in Yemen, his purges of princes, his torture of activists. And his murder of Jamal Khashoggi.

Khashoggi was 59 at the time of his death. He will be forever 59. The rest of us get older. But not all of us learn as we do.

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