As President Trump schools the Davos toffs in the realities of international relations, he is a tad handicapped by at least one bit of unfinished business: the red line he drew for Iran’s rulers.

It’s been nearly three weeks since the president first warned that if the Islamic Republic “violently kills peaceful protesters, which is their custom, the United States of America will come to their rescue,” tough words he echoed time and again.

And there’s not much ambiguity in comments like we’re “locked and loaded” or “they’re going to have to pay hell” — let alone his telling the protesters “help is on the way.”

Now it’s been over a week since Trump said he’s holding off in part because Tehran’s not (yet) executing protesters.

“Iran canceled the hanging of over 800 people,” he said, and he “greatly respected” that move.

Yet the regime has shut down the internet to stymie the public’s communications and flooded cities across Iran with Revolutionary Guard troops, Basij paramilitaries and foreign Arab fighters brought in from Lebanon and Iraq — that last one a clear sign that the powers-that-be fear regular Iranian troops won’t fire on their fellow citizens.

What limited news gets out suggests it is still creating plenty of martyrs — and charging families of its victims thousands to get their loved ones’ bodies back.

We don’t for a minute think he’s cowed by the regular, empty bluster from one regime figure or another about how Iran will respond if Trump makes good on his promises: Tehran did next to nothing after he took out its nuclear program, and has little capacity to do more now.

Tellingly, he said Saturday: “It’s time to look for new leadership in Iran,” adding that it’s time for “sick” Ayatollah Ali Khamenei to go.

Trump is “a man of action,” US Ambassador Mike Waltz warned at the United Nations last week.

Asking Trump to speak out as the new year began, we urged him: “Don’t be like President Barack Obama, who time and again flinched from publicly siding with Iranian protests, hesitating even to denounce Tehran’s bloody suppression of them.”

And speak out he did, as noted above.

But Obama set another terrible precedent in the Middle East by drawing his infamous “red line” in Syria, vowing he’d act if that regime used chemical weapons against its own people — but reneged when Bashar Assad did just that.

That debacle exposed Obama’s fundamental weakness; it’s no coincidence that Vladimir Putin’s first invasion of Ukraine, and seizure of Crimea, soon followed.

If there is also a wider lesson of the last half-century of mullah rule in Iran, it is that there is no deal that can be done with the theocracy — one with the stated aim of “Death to America.”

For that reason, a strike on the despotic regime is America First. 

Reporting suggests the USS Abraham Lincoln carrier strike group is steaming to the region and will arrive by the weekend. 

So we hope it is a case of when, not if, Trump attacks, for the sake of the protesters he encouraged and the wider world.

Trump has demonstrated plenty of toughness, so breaking his word to the people of Iran won’t make him look as craven as Obama.

But it will lead allies and adversaries to take any future threats with a Tehran-size grain of salt.