He took the United States out of the nuclear agreement and imposed sanctions against Iran — which some see as setting off a crisis that continues today — on claims that it was “on the cusp” of acquiring nuclear weapons “in just a short period of time.”

But international inspectors and United States military leaders said that Iran was complying with requirements to freeze its nuclear development.

Without a clear explanation for Mr. Trump’s behavior, anyone whose job requires forecasting the next American action — from foreign head of state to think tank analyst — was left guessing.

Deepening the challenge, the administration followed up with a set of demands that included some nuclear restrictions but focused mostly on Iran’s regional influence and proxy forces, ordering Tehran to sever ties to nearly all of them in a sweeping surrender.

Was this the real agenda? If so, what were the plans for winning each demand, and the metrics for measuring whether those plans were working? How would the administration balance competing priorities?

American action on the ground deepened confusion.

United States diplomacy has emphasized calls for peace but has conspicuously declined to offer what diplomats call “offramps” — easy, low-stakes opportunities for both sides to begin de-escalating, which are considered essential first steps.

“There’s been no talk of, say, ‘If you do this, then we’ll bring back waivers,’” Ms. Kaye said, referring to American waivers allowing other countries to buy Iranian oil. “‘If you do X, then you’ll get Y.’ There’s been nothing tangible like that.”