When the United States and Israel launched their war on Iran in late February, the regime in Tehran was in an unprecedented position of weakness. It faced existential economic and environmental crises, diminished defensive capabilities, and internal turmoil and external scrutiny following a brutal January crackdown on protests that killed thousands of its own people. But after 40 days of war and two months of shaky cease-fire, the Islamic Republic has emerged intact, emboldened, and armed with a new deterrent that appears even more powerful than all the weapons its adversaries damaged with airstrikes: its control over the Strait of Hormuz. In late April, U.S. Secretary of State Marco Rubio acknowledged that the strait had become Iran's “economic nuclear weapon.” The world now understands that if Iran is attacked, it will shut the strait, disrupting energy markets worldwide.

Put plainly, U.S. President Donald Trump lost both the war and the negotiations to end it. But if Tehran overplays its hand, it could lose the peace that follows. The memorandum of understanding that Iran and the United States are set to formally sign, the text of which Washington released on Wednesday, postpones the resolution of most of the difficult issues (including restrictions on Iran’s nuclear program) to a 60-day negotiating period. But the situation in the Strait of Hormuz will be far more difficult to finesse than most realize. The MOU will provide for the safe passage of commercial vessels at no charge for 60 days while Iran and, presumably, the United States seek to define the strait’s postwar administration. But whether a final deal is struck or not, Iran has made clear that it intends to impose new restrictions and fees on commercial vessels transiting the Strait after the negotiation period ends. Iran’s lead negotiator, Speaker of the Parliament Mohammad Ghalibaf, said outright that “the Strait of Hormuz will never return to its previous condition” and “naturally, we will charge fees in return for the services we provide.”

It is understandable why such an arrangement would tempt Iran. The country suffered immense economic damage during the war, and it is eager to quash any lingering notions that it is weak. But pressing for a status quo that does not fully open the Strait of Hormuz to all maritime traffic without fees or tolls risks undermining Iran’s newfound deterrence and makes a return to conflict more likely. It could upend global shipping permanently and, by accelerating the world’s effort to find alternative routes, lower the costs Iran’s adversaries face in launching a future war. The Strait of Hormuz could thus become the locus of postwar instability. And just as Trump overestimated his strategic advantage when he launched the war, Tehran could be poised to make the same mistake now that the war has........

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