Yet after leaving the summit, Mr Trump tweeted that he would instruct U.S. officials not to endorse the G7 statement, after objecting to comments from summit host Mr Trudeau.
The statement added "France and Europe maintain their support" for the G7 conclusions. "Our Tariffs are in response to his of 270% on dairy!" a second tweet read. He described Trudeau's news conference as "sophomoric" and a "political stunt".
Trump has infuriated the European Union, Canada and Mexico by imposing tariffs on steel and aluminum imports.
Mr Maas said: "It's actually not a real surprise, we have seen this with the climate agreement or the Iran deal".
Trump also targeted Trudeau on Twitter this weekend after the talks, saying Trudeau's "false statements" led him to decide not to sign the G7 communique.
In the week leading up to the the G-7 Summit President Trump engaged in the most Trumpian sort of diplomacy: he very publicly attacked out closest allies. So, I ask you: "He gets up in the airplane and leaves, and then Trudeau starts blasting him at a domestic news conference?" he asked CNN's Jake Tapper.
"If they retaliate, they're making a mistake", Trump said.
At the news conference, Trudeau said it was "kind of insulting" that the USA implemented tariffs on the basis of national security.
"The Prime Minister said nothing he hasn't said before - both in public, and in private conversations with the President".
A New York Times reporter who was present at the Trudeau press conference tweeted Sunday that he didn't understand what remarks Kudlow was referring to when the economic adviser said Trudeau stabbed the U.S.in the back.
Kudlow also insisted that Trudeau's remarks were created to make America look weak as Trump flies to Singapore for his meeting with North Korean dictator Kim Jong-un.
Der Spiegel, the German weekly, called Trump's performance in Quebec "a scandal without precedent" and said that German Chancellor Angela Merkel and other traditional United States allies must now be prepared for anything - especially on trade, a topic dear to German hearts.
The latest condemnation of Trudeau followed Trump's decision to not sign a G-7 communique after a weekend meeting of the seven largest industrialized economies, a group of traditional USA allies.
Reacting to Mr Trump's tweets, Mr Trudeau's office said: "We are focused on everything we accomplished here at the summit".
But Mr. Trudeau also said it was "kind of insulting" the USA had imposed tariffs on steel and aluminum under the guise of national security, noting Canadians stood "shoulder to shoulder" with Americans in overseas wars. Member countries made a decision to expel Russian Federation in 2014 after it annexed Crimea from Ukraine.
"The European Union is brutal to the United States".
The fight isn't just with Trudeau and Canada but with the best allies of the U.S., Democratic Senator Dianne Feinstein of California said on CNN.
The G7 countries, in the communique, "acknowledge free, fair, and mutually beneficial trade is a key engine for growth and jobs", and commits these nations to modernize the World Trade Organization (WTO).