When President Trump withdrew the United States from the Iran nuclear deal back in May, the foreign-policy establishment was unanimous in its opposition.

Their dismay was rooted in loyalty to Barack Obama’s legacy and personal contempt for Trump. But there was at least one point the critics made that seemed irrefutable, in warning against the re-imposition of US sanctions on Iran’s oil exports.

Trump’s unilateral move would certainly fail because of the interest of America’s European allies as well as the Russians and Chinese in continuing to do business with Iran. But if by some chance it worked, the experts were sure that would result in a severe hike in oil prices that American consumers would feel at the gas pump.

But the experts were wrong. Reports in Bloomberg News, echoed by The New York Times, tell us that three months into the new sanctions — and less than two months before the Trump administration plans to implement even more far-reaching restrictions on doing business with Iran that will affect US allies — the move has succeeded in crippling Iran’s oil exports without causing a significant increase in oil prices.

Iran’s principal source of foreign exchange is drying up, ratcheting up the pressure on an unpopular despotic regime without Americans having to pay appreciably more for gas.

How is that possible?

The answer is obvious, and it explains why the Obama negotiating strategy — resulting in an agreement that allowed Iran’s rogue state to keep its nuclear program and its ability to eventually create a bomb, while also enriching it — was so wrongheaded. In 2013, Obama relented just when sanctions were starting to bite and what followed was a strategic victory for Iran that brought it victory in Syria as well as a cash windfall to the tune of over $100 billion.

The Obama administration was guided by two critical false assumptions.

One was that the only way to limit Iran’s nuclear ambitions, ballistic-missile program or role as the world’s leading state sponsor of terrorism was to work in concert with US allies as well as Russia and China. Obama and former Secretary of State John Kerry were sure that the United States could achieve nothing acting on its own and allowed countries with a greater interest in commerce with Iran than in stopping it to exercise a veto over US policy.

The other assumption was that Iran was too strong to be brought to its knees even by international sanctions. That meant Obama and Kerry saw the only choices available to the West were either war or appeasement.

So they punted on any effort to link the nuclear issue to missiles or terrorism and ultimately made concession after concession in the negotiations that wound up giving the Iranians pretty much everything they wanted while the West swallowed a terrible bargain.

But it turns out that the Iran hawks in Trump’s new foreign-policy team — Secretary of State Mike Pompeo and National Security Advisor John Bolton — understood the situation better than the “adults” who urged the president not to scrap the nuclear deal. Rather than allow weak-willed allies to dictate US policy, Trump realized he could tell the appeasers what to do and make it stick because of the power of the US economy.

The shift in energy markets that led to the world being awash in oil — including the fact that the United States is now a net exporter rather than dependent on foreign sources — also means Iran has little leverage over the West.

The implications are clear.

Far from a hopeless quest, the US determination to force Iran to renegotiate the nuclear issue, cease its illegal missile program and desist from terror is a realistic goal.

Just as important, though Trump didn’t enter the White House with much knowledge of the subject, this vindicates his instincts that the establishment is intellectually bankrupt. For decades it has guided US Middle East policy on both Iran and Israel.

The success of oil sanctions should not only encourage the United States to push Tehran harder. It’s also one more reason to ignore the so-called experts’ contempt for Trump’s unconventional but clearly spot-on approach to the region.

Jonathan S. Tobin is editor in chief of JNS.org and a contributor to National Review.