By early fall, the deal was headed into the rough. Lawmakers in the European Parliament—rattled by Trump’s renewed talk of acquiring Greenland—questioned the durability of any agreement tied so closely to Trump’s coercive and shifting demands. Inside the Trump administration, officials were already discussing a far steeper tariff regime—up to 50 percent—if Europe didn’t yield, two U.S. officials told me. This month, after German Chancellor Friedrich Merz said the U.S. was being “humiliated” by Iran at the negotiating table, Trump accused the EU of backsliding on the deal and threatened new duties of 25 percent on European cars, an escalation that was poorly received in Brussels. “A deal is a deal, and we have a deal,” European Commission President Ursula von der Leyen said recently. “And the essence of this deal is prosperity, common rules, and reliability.”

Reliability. It’s a word I hear constantly from officials around the world when the conversation turns to the Trump administration—and especially, these days, the Iran war. In the past, Trump supporters, and even many U.S. allies, viewed Trump’s famous unpredictability as unorthodox but at times effective, a useful means of wrong-footing opponents or shaking up the tired status quo......

But that new sense that Trump is unreliable, the officials told me, has slowed efforts to end the war and reopen the Strait of Hormuz, because U.S. allies and Iranian negotiators don’t know whether to believe U.S. diplomatic outreach or the president’s apocalyptic comments (which on Thursday included an apparent threat of nuclear war). Longtime U.S. allies have accelerated their efforts to find alternatives to American leadership, especially because Trump’s goals in Iran haven’t been met and the global economy continues to suffer the war’s consequences. U.S. standing has also been eroded as Washington seeks to renegotiate the terms of trade with China, an effort that Trump will seek to kick-start with a visit this week. For Beijing, which has endured years of stop-and-start negotiations with Washington, Trump’s trip is a test of whether a functional working relationship between the world’s two most powerful countries is still possible......

Chinese officials have spent years adapting to Trump’s style. During his first term, Beijing often treated Trump’s unpredictability as a negotiating tactic—disruptive, but manageable. This time, the concern is different. Chinese officials and policy advisers question whether commitments made by Trump, his Cabinet, or U.S. negotiators will survive the next social-media post, tariff threat, or sudden reversal, according to U.S. and foreign officials (although U.S. officials say Beijing’s wavering is often to blame when agreements don’t materialize). Even before Trump’s trip, the administration has sent mixed signals on tariffs, semiconductor controls, and the scope of any broader trade détente.....

Robert Malley, a lead negotiator on the 2015 Iran nuclear deal—the Joint Comprehensive Plan of Action—who later served in the Biden administration, told me unpredictability can be an asset in negotiations by instilling fear and urgency in the other side. “But when unpredictability veers toward unreliability, the asset quickly can become a liability,” he told me. “At that point, the other side doesn’t so much have fear as lack of confidence, and it loses motivation for a deal because it can’t trust that a putative agreement can stick.” The likely outcome, Malley warned, “is chaos.”

What comes next is heavily contingent on how this war ends. Despite the unpopularity of Trump’s overseas military adventurism with his core supporters, the president has his eye on Cuba next. After Trump’s first term, many global leaders were keen to return to a business-as-usual approach when working with Washington. Trump’s second term has changed that. Finding ways to survive and thrive without heavy reliance on the U.S. is the new imperative.