President Trump is facing his trickiest diplomatic dilemma to date: how to punish a wayward ally, Saudi Arabia, without strengthening its regional foes — particularly American enemies, like Iran.

This is a far bigger issue than, say, Mr. Trump’s crude tweets or past real-estate deals between him and the Saudis. Decent people everywhere are appalled at what now clearly looks like a palace-sanctioned killing of Jamal Khashoggi — a former regime insider turned critic, and a supporter of the Riyadh-hated Muslim Brotherhood.

The gory details are being amplified by DC institutions like The Washington Post, which justifiably is demanding stiff punishment for the killers of its guest columnist, who cultivated ties with the town’s Who’s Who.

That, though, is not the whole story. As Iran smells blood in the water, its Western cheerleaders are advocating ending America’s alliance with Riyadh. Hence the delicate diplomatic dance.

Tuesday, Secretary of State Pompeo was in Riyadh, trying to finesse a coordinated response that would show our revulsion but not end the alliance or empower Iran. One possible solution: the Global Magnitsky Act, a congressional punishment exacted on officials perpetrating human-rights atrocities, rather than on their countries.

Sure, it’s a fudge. The current Saudi monarch, and even more so his son, de facto ruler Mohammad bin Salman, are like King Louis XIV’s “l’etat c’est moi” — they are the state. It may be hard to separate the country from the individuals.

Yet a fudge of some sort may be necessary to prevent Saudi regime chaos, leading perhaps to its eventual collapse. We see too much of that nowadays across the Mideast, and Tehran couldn’t be more pleased if that happened in the kingdom.

Price hikes at the pump, for example, sparked by an interruption in Saudi oil production, could pressure America to forgo oil sanctions against Iran, which are scheduled to kick in in a few weeks. Also, with Riyadh in turmoil, a key Arab leader in the resistance to Iran’s regional expansion would be weakened significantly.

Suddenly exposed to Saudi shenanigans, many Americans forget Iran is no better. As public opinion against the Saudis builds, Iran’s Western allies push for America to rethink Mr. Trump’s decision to pull out of the Obama-era nuclear deal with Tehran.

As former Deputy National Security Adviser Ben Rhodes claimed in the Atlantic, Mr. Trump only canceled that deal because of his “opposition to Obama and alignment with MbS, MbZ [the United Arab Emirates’ Mohammed bin Zayed] and the Netanyahu government in Israel.”

Mr. Rhodes rails against Saudi Arabia for its, for example, aimless and indiscriminate bombings in Yemen. Really? Mr. Rhodes was the architect of Obama’s studied blindness to atrocities committed by Iran, Russia and the Assad regime in this century’s cruelest war, in Syria. Yet he’s broken-hearted over Yemen?

MbS’s critics are correct: Killing Khashoggi increasingly looks like state-sanctioned terror. It was cruel and sloppy. That kind of thing isn’t unique to Saudi Arabia. The Iranian regime, recall, was launched with the seizure of 52 US diplomats, who were held hostage for 444 days; it’s kept American hostages ever since.

Tehran’s Lebanese puppet, Hezbollah, bombed the Marine barracks and the American embassy in Beirut. Iran inspired bombings in Buenos Aires and shootouts against Israeli and Jewish targets in Bulgaria, India, and Georgia. We did nothing to punish Iran after exposing an assassination attempt against the Saudi envoy in Washington.

Meanwhile, Turkey, where Khashoggi was killed, is leading the world in imprisoning journalists. While it fumes against the Saudis, Ankara has kidnapped, and at times killed, opposition figures for years.

None of that, of course, exonerates Riyadh. But as the Foundation for Defense of Democracies’ Iran-watcher Behnam Ben Taleblu says, “Many of those who’ve been silent on Iran’s human-rights abuses or use of terrorism abroad are now keen to see a crisis with our Gulf partners spiral out of control.”

That’s why the Khashoggi affair is so tricky, and why, in Riyadh, Mr. Pompeo had to struggle to utter the least inflammatory statements he could get away with.

Punishing MbS and his underlings is absolutely necessary. America must deter such behavior and show its revulsion. Yet Saudi Arabia hasn’t been a paragon of human rights at any time during our century-old alliance. Meanwhile, the Iranian regime chants “death to America” and behaves as badly as the Saudis, or worse. Tehran mustn’t emerge as a winner from our justified outrage against Riyadh.

This column first appeared in the New York Post.