“What Merkel is viscerally remembering was the American-European partnership at its height, in a period of emergency and world crisis,” said Philip D. Zelikow, who advised Mr. Bush on German reunification and the breakup of the Soviet Union. “Now here were are, as the system these leaders created is drifting into great jeopardy.”

“What exactly is the partnership that is managing this now?” he asked…

Some analysts argue that it is pointless to pine for the restoration of the American-led international order that Mr. Bush helped create. That system was beginning to fray well before Mr. Trump took office, for all sorts of reasons unrelated to him, and it is likely to keep unraveling, regardless of who follows him into the White House.

“This is essentially the old adage about generals always fighting the last war,” said John C. Kornblum, a former American ambassador to Germany who now works as a consultant and commentator in Berlin. “There is nothing to save. We are already deeply into the new order.”