Ambiguity—vague language, mixed messaging, frequent policy shifts—has been a hallmark of the United States’ approach to the war in Iran. From almost the moment the conflict began, U.S. President Donald Trump has vacillated over its purpose, what risks he might be willing to take, and what the United States would consider victory. He has threatened to destroy Iranian civilization, then promptly signed a cease-fire agreement. He has floated the possibility of taking Kharg Island, the hub of Iran’s oil industry, only to quickly walk it back. And he has discussed imposing a 20 percent toll on shipping through the Strait of Hormuz, only to declare that the waterway must be free to everyone.

In some cases, ambiguity can help countries settle wars. Leaders, for example, can leverage uncertainty to de-escalate a conflict or reach a stable peace agreement by letting both sides claim victory. If governments avoid drawing clear redlines, they can avoid pressure to escalate in response to attacks, creating space to cool tensions.

But Washington’s mixed messaging about the war in Iran has done more harm than good. Trump’s spectrum of threats, for example, prompted Tehran to see the war in existential terms and maximally fight back. The lack of clarity over the status of the Strait of Hormuz made the June memorandum of understanding negotiated by the two countries impossibly frail. To reach a more durable truce, the Trump administration needs to be clearer about its goals and more consistent in pursuing them. Otherwise, Iran and the United States will continue to get their wires crossed—and the next cease-fire could again collapse.

When coercing a rival, a government must decide how to convey intent, capabilities, and redlines. One option is to be clear: explicitly and consistently defining a goal, identifying consequences for noncompliance, and articulating what the other side can count on if demands are met. Such clarity can let a rival state know what is at stake and encourage it to limit its response. But too much of it can do the opposite. If the rival knows just how far it can go toward a threshold without triggering retaliation, it will often escalate all the way to that point.

The other option is to be vague. Yet this can also have mixed consequences. If a state does not know how its adversary will respond to a certain action, it might hold back for fear of triggering painful counterattacks. But too many mixed signals can throw off an opponent’s risk calculus, giving rise to misunderstandings that can produce or worsen a crisis.

This is what happened with the United States’ Operation Epic Fury—its military operation against Iran. Trump has variously said, at different times, that the goal of the campaign is to degrade........

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