But the fissures in the American-led anti-Iran coalition, exemplified by the secretive Emirati-Iranian talks, have dimmed a vision of a realignment in the Middle East long advocated not only by Mr. Trump, but also by the leaders of the Arab states in the Persian Gulf and Prime Minister Benjamin Netanyahu of Israel. In that vision, Israel and certain Sunni countries gain supremacy over Iran, the world’s largest Shiite-majority state.

Iranian officials also miscalculated, believing that after a series of escalatory military operations — the tanker attacks, the shooting down of an American drone, the Saudi oil strikes, rocket attacks on bases in Iraq by Iranian-backed militias — Mr. Trump would refrain from responding consequentially. Instead, he made the startling decision to authorize the killing of General Suleimani.

“There were dueling perceptions both in Tehran and in Washington that the other side was a paper tiger,” said Karim Sadjadpour, an Iran expert at the Carnegie Endowment for International Peace.