Another senior European official told me: “The fear is the sequence: A bad NATO summit followed by a good Putin meeting with the two leaders embracing.”

The official said he worried that Trump would repeat what he did at the G7 in Canada: provoke a fight with his closest allies and then lavish praise on a dictator as he did on Kim Jong-un in Singapore following the G7.

Other sources told me they’re fretting about what other concessions Trump might make. They’re hoping he doesn’t make any spontaneous promises to Putin over Syria or sanctions.

European officials aren’t sure about the exact timing of the Trump-Putin summit — or whether it will happen just before or after the NATO summit. Either way, they’re worried about the contrast between a warm meeting with Putin and clashes with NATO allies over issues like defense spending.