President Trump wasted no time after tying a bow on his meeting with Kim Jong-un to finally punch back, so to speak, at the actor Robert De Niro, who spent the last couple of days publicly slamming the president, going as far as to use profanity during the Tony Awards on Sunday night.

“____ Trump,” Mr. De Niro shouted into the microphone on Sunday, before introducing Bruce Springsteen. “It’s no longer ‘Down with Trump!’ It’s just ‘____ Trump!’” he said. The crowd gave him a standing ovation. Mr. De Niro flexed both of his arms.

At an event in Toronto on Monday, Mr. De Niro apologized to Prime Minister Justin Trudeau of Canada, and to others who attended the Group of 7 summit meeting in Quebec last week, for what he called the president’s “idiotic behavior.”

President Trump had refused to sign a communiqué at the summit, and called Mr. Trudeau “dishonest” and “weak” in a tweet afterward. Mr. De Niro said Mr. Trump’s behavior was “a disgrace” and “disgusting.”