A few minutes following President Trump and Chancellor Merkel's remarks at the NATO memorials ceremony, the leaders of NATO countries walked onto a three-tiered stage in the lobby of the new NATO headquarters to pose for their family photo.
President Trump stood at the front/lowest tier, in the center, alongside the NATO Secretary General Jens Stoltenberg to his right and British Prime Minister Theresa May to his left.
Some of the leaders interacted with one another on stage, but not Trump. He stood silently, shifting his stance at moments and looking around.
Canadian Prime Minister Justin Trudeau said, "Everybody wave!" encouraging his counterparts to wave for the cameras. Some followed Trudeau's command, but not Trump, who did not raise an arm.
Trump smiled for a brief moment, but otherwise kept a serious, perhaps even stern, expression on his face for the duration of the photo opp.
When the photo opp concluded, Stoltenberg helped show Trump the way off the stage. Merkel stayed on stage for a few minutes as other leaders, including French President Macron, came up to mingle with her. Your pooler did not see any leaders approach Trump or talk with him on his way out.