The negotiators included agree-to-disagree language on climate change and on an international commitment to reduce plastics in the world. And then the statement was released on Saturday night, only to have Mr. Trump disavow it. Mrs. May learned only as her helicopter arrived at the airport for her to board her plane to return to London.
“It started out as a good summit because we were actually talking to each other, instead of past each other,” said Peter Beyer, the German government’s coordinator on trans-Atlantic relations. But he added, “It looks like the U.S. is no longer a reliable partner in international agreements, and that’s bad.”
Josef Braml of the German Council on Foreign Relations said Mr. Trump considered diplomacy a waste of time. “He is about to destroy what’s left of the liberal world order because he thinks rules and institutions help America’s rivals, China and Europe,” he said.
Laurence Nardon, director of the North American program at the French Institute of International Relations in Paris, said Mr. Trump’s behavior was a negotiation trick. “It’s like when a person leaves the room and slams the door, but is hoping the other person will run after them and follow them into the corridor,” she said.
In Washington, Democrats and some Republicans were upset at the outcome. But Mr. Trump received support from a few Republicans.
Representative Tom Cole, Republican of Oklahoma, called some comments by Mr. Trump’s aides “a little over the top” but faulted Mr. Trudeau for taking “shots after the G-7 on the eve of an American president sitting down with North Korea.”
Representative Peter T. King, Republican of New York, called the episode a “warning shot to Kim Jong-un” in keeping with Mr. Trump’s approach to negotiations. “This is the Trump style of getting things done,” he said. As to the wisdom of such a public clash, he said, “It depends on how it turns out. This president lives on a high wire, and so far it’s been working.”