Kudlow said the president won't "let a Canadian prime minister push him around". Larry Kudlow, Trump's chief economic adviser, told CNN that Trudeau's press conference addressing Trump's actions was "a betrayal".
"Canadians are polite and reasonable, but we will not be pushed around", Trudeau said.
Mulroney's role as a former prime minister advising an opposing party is unique to him throughout Canada's history and is indicative of the alignment between the two main federal parties over the trade file. Some of Trump's aides also lashed out at the Canadian prime minister. However, she suggested the government should look at means of increasing trade and co-operation with other Atlantic Canadian provinces, in light of the looming trade spat with the U.S. So Trump's national security justification is so laughable that Republicans who have been willing to stick by Trump through every other blunder are ready to work with Democrats to block these tariffs by holding military spending hostage.
"He really kind of stabbed us in the back", he said.
Mr Trump's advisers said the United States president believed he had been stabbed in the back by Mr Trudeau over USA tariffs.
"Fair trade is now to be called fool trade if it is not reciprocal", said Trump, who flew from Canada to Singapore on Sunday to prepare for the first-ever summit between a USA and North Korean leader.
Merkel says differences on trade remain despite joint G7 communique
Despite this, they were seen to be on good terms, and President Macron's team said his talks with Trump were "frank and robust". The other G7 leaders met without Trump for the rest of the day, discussing climate change and global development.
Trump said he was retaliating against Canada with countervailing tariffs, saying of Trudeau: "He learned that's going to cost a lot of money for the people of Canada".
The Group of Seven meet over the weekend saw much drama, opening up the possibility of a trade war, but what stole the show on social media were Canadian Prime Minister Justin Trudeau's eyebrows.
People close to the situation said they were disappointed the outreach had not been as productive as they hoped.
A Trudeau spokesman, Cameron Ahmad, said on Saturday night that Mr Trudeau "said nothing he hasn't said before - both in public and in private conversations" with Mr Trump.
Earlier today, Trudeau cheered Trump's bid to broker a deal to rid the Korean Peninsula of nuclear weapons, but he stayed mum on the US administration's persistent trash talk.
Trump made his comments in a wide-ranging news conference in Singapore following his historic summit with North Korean leader Kim Jong Un.
Trump has consistently railed against what he claims are unfair trade practices by some of America's biggest trade partners, including Canada - in particular Canada's supply management system, which levels tariffs of up to 300 per cent on imported dairy products.