Once the dust settles over the fate of Saudi columnist Jamal Khashoggi, who disappeared inside the Saudi consulate in Istanbul last Tuesday and is rumored to have been murdered by agents of Riyadh, America must respond — carefully.

Killing Khashoggi — a Saudi dissident and Washington Post columnist who resides in the U.S. capital — is, if true, a horrific act of state terrorism and hostility to America. It certainly deserves reexamining our relations with King Salman and his son, the self-styled “reformist” Mohammed bin Salman.

It would also be a reminder that the kingdom has never been a paragon of human rights or benevolent governance. Our century-old alliance is based on mutual interests, not shared morality.

The Istanbul disappearance mystery is, for now, roiled by unnamed supporters of President Recep Tayyip Erdogan (no other sources are available in today’s Turkey), who told Reuters that Khashoggi was murdered by Saudi operatives and dismembered to be smuggled out of the consulate while his fiancée waited outside.

A word of caution: Turkey is tight with a Saudi regional foe, Qatar, and has increased trade relations with Iran, an even bigger Saudi enemy. Also, Mr. Erdogan arrests domestic foes by the wagon loads and is currently holding an American citizen, Andrew Brunson, hostage. He has an incentive to make the Saudis look bad, help his allies and make himself look less bad in comparison.

Yet the story is plausible. Once a Saudi insider, Khashoggi has become a harsh critic. Worse, his reports on regime misdeeds were made in Washington, where Riyadh invests huge sums of money to launder its image as a benevolent American ally

As Khashoggi detailed, MBS ruthlessly silences domestic foes. The infamous Riyadh Ritz-Carlton incarceration of relatives on embezzlement charges was a harbinger of the king-to-be’s penchant for disappearing foes into dungeons while he consolidates power.

So even if Khashoggi wasn’t assassinated — some speculate he was “just” hustled from Istanbul to a cell in Riyadh — the Saudis must provide an explanation.

For his part, MBS told Bloomberg News that Khashoggi is “a Saudi citizen and we are very keen to know what happened to him.” But since the columnist was last seen entering a Saudi diplomatic facility, that’s simply not good enough — not even close.

“I pray Saudi journalist Jamal Khashoggi is alive,” Senator Marco Rubio tweeted Sunday. “But if this deeply disturbing news report is confirmed, the United States & the civilized world must respond strongly, and I will review all options in Senate.”

What to do?

President Eisenhower once said Nicaragua’s dictator, Anastasio Somoza, “may be a son of a bitch, but he’s our son of a bitch.” MBS may be a clueless son of a king, but he’s our son of a king.

So yes, America must be a defender of human rights and liberty, but we should know an ally from foe: Unlike in some other Mideast countries, no one in the streets of Riyadh chants “death to America.”

Yet if the worst about Khashoggi is true, America must publicly rebuke MBS and threaten future sanctions. The right kind of pressure can also enhance American interests.

Example: President Trump wants the Saudis to contribute more to their own defense, saying, in his normal hyperbole, the kingdom wouldn’t last a day without America. So Mr. Trump should take this moment to remind the Saudis what a true alliance with America looks like.

That should be followed by a demand that Riyadh calm energy markets by making clear it’ll significantly increase pumping to offset our Iran oil sanctions, which kick in next month.

Also, when the White House releases its Israeli-Palestinian peace plan, the Saudis must vocally support it. The plan is reportedly premised on Arab states’ tightening relations with Israel, yet King Salman said he would follow Ramallah’s cue instead. The kimg should use this moment to change course, pressure Palestinians to stand down on their excessive demands, and even make public some of its clandestine ties with Israel.

Speaking of peace, Riyadh should end its dispute with Qatar and revive a united pro-American Gulf alliance.

Last, the Saudis must significantly ease domestic repression and allow more legitimate criticism. This could serve MBS’s reform ambitions better than strong-arm tactics — though he may fear the long knives are already out for him. But if he’s caught assassinating an American columnist — and that’s still an if — he’ll need to be reminded what his fortunes would look like without a superpower in his corner.

This column first appeared in the New York Post.