One source asked by CNN whether the comment was meant as a joke replied: "To the degree one can ever take what is said as a joke".
"A trade war doesn't spare anyone".
And ahead of the summit he went on Twitter attacking the European Union and his Canadian host Prime Minister Justin Trudeau.
"It is simply ridiculous to view any trade with Canada as a national security threat to the US", Mr Trudeau has said of the move.
"The trade gap will narrow if we are allowed to export more to all these countries", Kudlow said. "The six countries of the G7 without the United States, are a bigger market taken together than the American market".
The allies themselves are planning to push back, both by imposing countervailing tariffs and by presenting a united front against the president's policies at the Group of 7 summit beginning Friday in Canada.
"It'll be very similar to other G7 tables in which we highlight and discuss many things that were agreed on and have differences of opinion on other things", Trudeau said.
He doesn't see the US tariffs as a specific attack against Canada or even Saguenay, but likely more of a strategic move by someone he considers a canny and experienced negotiator. "The impact on Canada and ultimately on workers in the USA won't be a laughing matter".
Trump responded by saying: "Didn't you guys burn down the White House?"
Trump's comments were his latest attacking key US allies ahead of the Group of Seven summit in Charlevoix, Quebec, which is set to begin on Friday.
Now, to be fair to Trump, the British attack on the White House was in retaliation for our attack on York, Ontario (a British colony at the time), but that's pretty much the only way that Canada is connected to this infamous act.
Macron said he's faced criticism that he's been too friendly with the USA president.
When Trudeau won power, the bedrock of his foreign policy was to return Canada to its traditional multilateral leanings - support for institutions such as the United Nations, NATO, the G7 and the global trading order.
Kudlow said allies should understand that Trump "will do what is necessary to protect the USA, its businesses and its workforce", adding that Trump "has always said, and I agree, tariffs are a tool in that effort".