After Trump had left the summit in Quebec he rounded on Justin Trudeau personally, suggesting the Canadian Prime Minister was "very dishonest and weak" and "acts hurt when called out".
Last month, Canadian Prime Minister Justin Trudeau announced his government would retaliate against Trump's tariffs by imposing import taxes on $12.8 billion worth of USA imports in what Canada says its strongest trade action since the World War II.
His tweet, shortly after leaving Charlevoix in Quebec, came in response to what he claimed were "false statements" by the summit host, Canadian premier Justin Trudeau.
"That's going to cost a lot of money for the people of Canada; he learned", Trump said wagging his finger.
But Trudeau still said a few things that didn't go down well inside Air Force One.
Mr Trump has consistently said that countries that have a trade surplus with the United States are "taking advantage". "Canadians, we're polite, we're reasonable, but we also will not be pushed around", Trudeau said, triggering a dispute that now revolves around three key issues.
The mysterious deaths of African ancient trees
They have been surveying the trees since 2005 and have developed a theory of how they grow, while also documenting the losses. They were surprised that most of the oldest and biggest died within those 12 years. "It's statistically very unlikely".
In particular, Canada, Japan and the European G7 powers are outraged by Trump's unilateral - or illegal, in their eyes - imposition of tariffs on imported steel and aluminum in the name of preserving USA industry on national security grounds.
Mr Trump also said he might double down on import tariffs by hitting the sensitive auto industry, throwing the G7's efforts to show a united front into disarray.
On Sunday, Trudeau ignored the barbs from Trump's advisors, tweeting a link to the G7 communique and hailing the "historic and important agreement we all reached".
Trump wrote on Twitter.
The European Union responded to the attack on Sunday evening, with European Council President Donald Tusk tweeting that Trudeau deserved a "special place in heaven" for organizing the G-7 summit. Thomas Wright, a senior fellow at the Brookings Institution, told reporters that for Trump's first 500 days, "these countries generally were bent over backwards not to criticize President Trump. They're gonna do what they can to defend and protect their country, just like we're trying to do the same thing with ours".
European officials said Trump had tried to water down the language in the draft communique on the WTO and rules-based trade.
Canada in particular has been outraged by Trump's tariffs, taking umbrage at the argument that they were motivated by national security concerns. In the end, that language stayed in and it was only on climate change that no consensus was reached.