With U.S. President Donald Trump and Prime Minister Justin Trudeau at the centre of the dispute, the back and forth has intensified since just before the start of the month - when the Americans imposed hefty steel and aluminum tariffs on Canada.
President Donald Trump shakes hands with Canada's Prime Minister Justin Trudeau in a bilateral meeting at the G-7 summit in in Charlevoix, Quebec, Canada, June 8, 2018. He said the Canadian leader must not have realized that Trump had televisions on Air Force One, allowing him to monitor Trudeau's news conference at the end of the G-7 summit. Kudlow's remarks followed a Twitter attack on Trudeau by Trump, as well as Trump's decision to withdraw from a joint communique that he had endorsed only hours earlier.
"POTUS is not going to let a Canadian prime minister push him around on the eve of this", Kudlow said on CNN in reaction to Trudeau's closing news conference at the summit.
U.S. President Donald Trump issued a volley of tweets on Monday venting anger on some of Washington's closest North Atlantic Treaty Organisation allies over the United State's trade deficit, following a divisive G7 meeting in Canada.
The president said he was annoyed by Trudeau's comments about not letting Canada get pushed around.
A Trudeau spokesman, Cameron Ahmad, said Saturday night that Trudeau "said nothing he hasn't said before - both in public and in private conversations" with Trump.
A Trump trade official, however, doubled down on the insult, saying there's a "special place in hell" for those who betrayed Trump.
Kudlow, the conservative economist who directs the National Economic Council, was upset with Trudeau's comments at a press conference after the contentious Group of 7 summit in Quebec.
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Canadian Prime Minister Justin Trudeau's eyebrow has become the unexpected star of the G7 summit, prompting online speculation after it appeared to slide down his face. He also attacked Trudeau's character, calling the Liberal Party leader meek, weak and dishonest.
On 1 June, the U.S. imposed a 25% tariff for steel and 10% for aluminium on imports from the European Union (EU), Canada, and Mexico.
"There is a special place in heaven for @JustinTrudeau". I'll tell you this to my friends in Canada that was one of the worst political miscalculations of a Canadian leader in modern Canadian history.
If there's anything that Trump learnt from the G7 Summit in Canada, it's that fair trade was a "fool trade".
G7 allies seemed as perplexed as Canada at the sudden diplomatic row, and Germany and France accused Mr Trump of destroying trust and acting inconsistently.
"According to a Canada release, they make nearly 100 Billion Dollars in Trade with USA (guess they were bragging and got caught!)".
The president fired back on Twitter, writing that Canada already charges a 270 percent tariff on dairy products.
Trump's actions are being called ludicrous and absurd - but then again, coming from a man whose only experience before entering politics was as a businessman (with highly questionable dealings and tactics) and a reality TV show host, might not be all that surprising.