The Europeans, meanwhile, have shared their worries widely ahead of the meeting. “All I’m hearing is great anxiety about what Trump might do or say,” said Ivo Daalder, who served as U.S. ambassador to NATO from 2009 to 2013.

“The last two NATO meetings didn’t go well,” Daalder told me. “In 2017, [Trump] refused to reaffirm Article 5, and in 2018, he threatened to walk away from NATO if Europeans didn’t spend more on defense.”

Article 5 guarantees that NATO allies will defend one another against an armed attack. NATO means nothing without this promise. After an outcry, Trump explicitly endorsed NATO’s mutual defense clause.

Between the lines: NATO Secretary-General Jens Stoltenberg has preemptively placated Trump. He released new data showing that allies are spending many billions more on their defense, which Trump has demanded.