Trump earlier had a working lunch with Singapore Prime Minister Lee Hsien Loong at the presidential palace Istana after their bilateral meeting during which the two leaders discussed everything from the summit preparations to the US' tariff threats.
Despite the tensions at the gathering in Canada, Mr Trump rated his relationship with their leaders as a "10" - naming Germany's Angela Merkel, French president Emmanuel Macron and Canada's Justin Trudeau, but not the UK's Prime Minister.
Trump called Trudeau "very dishonest and weak" on Twitter on Saturday and then sent Kudlow and trade adviserPeter Navarro to hammer the message home on Sunday morning news shows in an extraordinary assault on a close US ally and neighbor.
Trudeau told reporters that Canada would move forward on July 1 with retaliatory tariffs to answer for Trump's tariffs on aluminum and steel that were "unjustly applied to us".
Trade disputes between USA and India have heightened, indicating that Trump's economic grievances are not restricted to the developed countries alone.
Trade adviser Peter Navarro told "Fox News Sunday" that "there is a special place in hell for any leader that engages in bad faith diplomacy" with Trump.
Nearly 18 months into Trump's presidency, Merkel's comments offered renewed evidence of Germany's struggle to adapt to an upended relationship with the US.
The leaders of some of the world's largest economies had worked late into the night to craft a final message from their meeting in Quebec, finding a careful balance between their concerns and Trump's, particularly on trade.
Trump's decision to withdraw his support for the communiqué has drawn sharp criticism from Germany on Sunday.
At the G-7 summit, Trump's spokeswoman, Sarah Huckabee Sanders, said the US was "close to a deal" on NAFTA.
Key to Trump's concerns appeared to be declarations on trade, a thorny issue following Trump's announcement that he planned to impose tariffs on steel and aluminum exports from the European Union, Canada and Mexico. "The European Union is brutal to the United States. We must put the American worker first!"
Less than 24 hours before his meeting with Kim, Trump found time to lambast what he sees as unfair trade practices among the other six industrialized democracies at the summit. Echoing a series of comments she's made about the erosion of US-European ties, Merkel expressed consternation about Trump's disavowal of the G-7's joint closing statement.
"Canadians are polite and reasonable but we will also not be pushed around", Trudeau said.
But Trudeau later contradicted the president: "We will not, can not sign a trade deal that expires every five years". He emphatically said that the United States was no longer going to allow that kind of imbalance.