A video of Justin Trudeau gossiping with other world leaders about Donald Trump is featured in an advertisement for the U.S. president's leading political rival.

"The world is laughing at President Trump," says the ad from former vice-president Joe Biden's campaign for the Democratic Party's presidential nomination. "They see him for what he really is: dangerously incompetent and incapable of world leadership."

The video, captured during a reception at Buckingham Palace, shows Trudeau chatting with the president of France and the prime ministers of the United Kingdom and the Netherlands about Trump's long impromptu press conferences. Shot by the host broadcaster at this week's summit of NATO leaders, the video shows Trudeau most clearly, at a distance but fully facing the camera.

"I just watched — watched his team's jaws drop to the floor," Trudeau says in the recording, eyes wide in imitation. He later said he was talking about Trump's unexpected announcement that the United States will host the next G7 leaders' summit at Camp David, an idea Trump had previously raised but not finalized.

Biden's ad combines the recording of Trudeau with footage from a speech Trump gave to the United Nations, where leaders and diplomats in the General Assembly laughed when the president said almost no U.S. administration had ever accomplished as much as his had. There are additional clips of him pushing past people at other events and awkwardly missing handshakes.

"The world sees Trump for what he is," Biden says as the advertisement ends, his voice laid over images of him with leaders including Trudeau. "Insincere, ill-informed, corrupt, dangerously incompetent and incapable, in my view, of world leadership."

The world is laughing at President Trump. They see him for what he really is: dangerously incompetent and incapable of world leadership.<br><br>We cannot give him four more years as commander in chief. <a href="https://t.co/IR8K2k54YQ">pic.twitter.com/IR8K2k54YQ</a> —@JoeBiden

The ad was released late Wednesday on Twitter and by mid-morning Thursday had already been viewed more than six million times.

Trump seemed to shrug off the recording of the other leaders in London as the NATO summit wrapped up, calling Trudeau "two-faced" but also overall a good guy.

His son, Donald Trump Jr., tweeted: "As usual @realDonaldTrump is 100% right!!!" along with one of the images of Trudeau in brownface, from when he was a teacher at a Vancouver private school. Those old pictures, from various performances and costume parties, haunted Trudeau's re-election effort when they emerged early in this fall's federal campaign. Trudeau acknowledged during the campaign that dressing up and darkening his skin the way he had was racist.

Trump sees Biden as such a political threat that he's facing impeachment over apparent attempts to get help from Ukrainian authorities to damage Biden's campaign and has reacted badly to having his dignity challenged.

Canada, the United States and Mexico are in delicate negotiations over a new continental free-trade deal, hoping to sand down rough edges that are keeping the Democrats, who currently control the U.S. House of Representatives, from allowing the United States-Mexico-Canada Agreement to go to a ratification vote.

Canadian priorities aren't central to the trouble — legislators' concerns about Mexico's environmental and labour standards are — but impeding the negotiations would be one easy way for Trump to seek satisfaction.