President George Bush meeting with Chancellor Helmut Kohl of Germany in the Oval Office on Sept. 16, 1991, shortly after the collapse of the Soviet Union. Greg Gibson/Associated Press

WASHINGTON — On Sept. 16, 1991, Angela Merkel, then a young protégé of Chancellor Helmut Kohl of Germany, watched in the Oval Office as her boss and President George Bush wrestled with the sudden collapse of the Soviet Union. Without an influx of emergency aid, Germans feared that refugees could pour across the border, threatening the stability of their newly reunified country.

Ms. Merkel shared that memory with President Trump at a summit meeting in Buenos Aires the morning after Mr. Bush’s death. Later, she told reporters, “Helmut Kohl could rely on this friend of the Germans in the White House.” If not for Mr. Bush’s sure-footed handling of those historic events, Ms. Merkel added, she “would hardly be standing here.”

With Mr. Bush’s death, a generation of Cold War leaders has passed from the stage. Of the major figures of that era, only Mikhail S. Gorbachev, the Soviet Union’s last leader, is still alive. But at 87, he is too ill to attend Mr. Bush’s funeral. Mr. Kohl died last year; even his protégé Ms. Merkel, who went on to become Germany’s first female chancellor, is now in the sunset of her political career.

Ms. Merkel’s reminiscences about Mr. Bush were all the more poignant, given that she was about to sit down with Mr. Trump, who grew up during the Cold War but has gleefully tried to dismantle the European and global institutions that Mr. Bush and his Cold War-vintage colleagues built.

“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.

It is easy to forget, as the tributes to Mr. Bush pour in, that these Cold War partnerships were not without their bumps. While Mr. Bush and Mr. Kohl agreed on the need for food and medicine for the Soviets, they differed over how quickly to provide economic assistance. Mr. Bush wanted the Soviets to undertake sweeping market-oriented changes first.

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.