“This is a no-brainer,” said Michael Carpenter, senior director of the Penn Biden Center for Diplomacy and Global Engagement and a former Pentagon official under Mr. Obama.
“It’s all about the political optics in light of the Trump Tower Moscow news and the fact that Trump simply can’t bring himself to ever confront Putin in public,” Mr. Carpenter said. “This would have been a P.R. disaster of epic proportions if he had agreed to meet and not confronted Putin.”
Once again, however, Mr. Trump’s ad hoc decision-making caught a foreign government unawares. Dmitri S. Peskov, the Kremlin spokesman, told Russian reporters that they had seen Mr. Trump’s Twitter posting but had no other word from the American government.
“We don’t have official information,” he said, according to the Tass news agency. He added, “If this is so,” then Mr. Putin “will have a few additional hours in the schedule for useful meetings on the sidelines of the summit.”
Other sub-dramas were percolating in Buenos Aires as Mr. Trump flew on Thursday. The president downgraded scheduled meetings with two allies, Presidents Moon Jae-in of South Korea and Recep Tayyip Erdogan of Turkey, without explanation. Instead of full-fledged sessions, the president will have “pull-asides” with both, according to the White House, meaning casual chats on the sideline of the main sessions.
At the same time, speculation focused on whether Prime Minister Justin Trudeau of Canada would attend the ceremonial signing on Friday of the revised version of the North American Free Trade Agreement, which Mr. Trump has rebranded the United States-Mexico-Canada Agreement. Mr. Trudeau’s schedule did not include the ceremony, but a Canadian official late Thursday confirmed that he would attend.
And then there was Chancellor Angela Merkel of Germany, who also has a tense relationship with Mr. Trump and was scheduled to meet with him on Friday. Her government plane was forced to land en route to Buenos Aires by technical difficulties and she was reported to be turning to a commercial flight on Friday, an embarrassment for the leader of a major power.