The measure of a successful Iranian dynasty has always been simple: For 2½ millennia, Iranians have judged their kings good if the kings managed to keep good order. Siyasat, the Persian word for politics, originally meant simply this.

By that yardstick, the current clerical “dynasty” has failed miserably.

Witness the latest wave of popular unrest engulfing the Islamic Republic. What began Friday as a protest against fuel subsidy cuts ignited into a full-blown uprising. Cries of “Death to dictator!” rang out from the streets, as did slogans decrying the Islamist regime’s foreign interventions (“Not Gaza, not Lebanon, my life only for Iran!”). Gas stations were burned, and video footage from the provinces suggested some local authorities had lost control.

President Hasan Rouhani — remember when the American chattering classes crowned him the great moderate reformer? — called it the most serious internal threat in the regime’s 40-plus-year history. And vowed to crush it.

The repressive apparatus responded with that famously gentle touch — completely shutting down internet access, deploying the ­vicious basij militias and killing more than 200 protesters in 21 cities, ­according to Amnesty International. In some areas, the security forces stood down after the people offered them flowers. But on the whole, the Islamic Republic once more revealed that its hold on power rests entirely on the force of arms and torture.

Whatever the course of events, and as of now it looks as if the ­regime has indeed managed to ­extinguish the uprising, one thing is clear: Four decades since it was founded, the Islamic Republic has wrought little but crushing poverty, eye-watering graft and unrelenting foreign tension. The regime metes out Chinese-style oppression without even delivering Chinese-style growth and development.

Regime ideologues can blame Western sanctions for their economic woes ’til they go blue, but the fact is, they have picked too many fights with too many neighbors — not to mention a certain superpower that can utterly cut off their state from global financial powers. They have built their Shiite crescent — stretching from the Arabian Peninsula to the Levant — on the backs of a hungry populace.

What good is a Syrian conquest when the ordinary Iranian sugar factory hand can’t afford meat and a dozen eggs? Or what good is effective suzerainty over Iraq when the Iranian public school teacher hasn’t been paid her salary for nine months straight?

Such contradictions have felled much mightier powers than the ­Islamic Republic of Iran, so the regime’s days are numbered, especially if President Trump is ­re-elected. That would mean the mullahs would have to withstand sanctions pressure, not for another year — but five.

The question, for the Iranians and us, is what comes next. Many in Washington dream of reviving the ailing spirit of the 1989 velvet revolutions in Iran. Don’t bet on it. The more realistic outcome — and desirable, if a fractious and ethnically divided country isn’t to fall into chaos in a region that has more than its share — is benign strongman or even monarchic rule.

Iran’s political culture has always had a living source of authority who embodies the national will. Iranians have always had a king. Their failed experiment with constitutionalism at the turn of the last century never dislodged ­monarchic power, and the current Islamic Republic also has a living symbol of national authority, a clerical “supreme leader,” a king by another name. Imagining a thoroughly republican Iran, or a thoroughly secular one, is the kind of liberal utopian folly that created the disaster in Iraq.

But even before Iranians get to the point of pondering a post-Islamic Republic order, they need a visible, living figure around whom they might rally in opposition.

The Pahlavi Dynasty, which forged the modern nation-state of Iran, had its Reza Khan (who later became Reza Shah). Likewise, the 1979 Islamic Revolution that toppled the Pahlavis and brought the current regime to power had its Ayatollah Khomeini (who later become the ­supreme leader). Today’s opposition needs such a figure to supply an ­answer to the question: Whom would you propose to rule us?

Could Reza Khan’s Maryland-based grandson, Reza Pahlavi, ­return to the Peacock Throne? Maybe. But don’t be surprised if the next king or supreme leader emerges from within the regime’s own security apparatus.

Sohrab Ahmari is The Post’s op-ed editor. Twitter: @SohrabAhmari