More than five months later, the war that Mr. Trump believed would be over in weeks, if not days, is far from over. Mr. Trump has alternated between strikes, ceasefires, talks, threats, ultimatums, renewed strikes, and U-turns in an attempt to shape the course and outcome of the conflict and the behaviour of the Iranian state, while seeking a face-saving exit. But with the war unresolved and his objectives unmet, Mr. Trump, confronting a resolute yet risk-tolerant Tehran, has found himself in a strategic cul-de-sac. Without toppling the Islamic Republic, achieving any of the other goals appeared impossible even before the war began. This makes regime change or regime collapse the central strategic aim of the war on which all the others depended.