Making the announcement on the Twitter social network, he accused Trudeau of "false statements", and being "Very dishonest & weak" in an extraordinary attack on the leader of one of the US's biggest allies.
In a tweet posted Saturday evening, Trump said his decision to rescind support for the statement was based on "false statements" made by Trudeau during a press conference he gave, as well as "the fact that Canada is charging massive Tariffs" on USA companies. The U.S. president seems to be alluding to a discordance between Justin Trudeau overall temperament during the meeting and his stance on U.S. Tariffs between the neighbouring countries. "And that's what bad faith Justin Trudeau did at that stunt press conference".
Kudlow had been negotiating nicely with Trudeau at the summit in Quebec and the United States had agreed to join the joint communique, but Trump pulled out after he felt betrayed by Trudeau's news conference where the prime minister called Trump's tariffs on Canadian aluminum and steel exports "insulting".
"He held a press conference and he said the United States is insulting".
The tweets will be a serious and completely unexpected blow to the French president Emanuel Macron and the German chancellor Angela Merkel, who believed a deal to smooth over tensins on US-European trade had been agreed.
"The world as we know it, namely the USA -led rules-based multilateralism, is now in serious danger of unravelling, as illustrated at the G7 meeting", said Erik Nielsen, chief economist at Unicredit Bank.
He said he just wants what's fair for America.
He followed up by tweeting: "PM Justin Trudeau of Canada acted so meek and mild during our @G7 meetings only to give a news conference after I left saying that, "US Tariffs were kind of insulting" and he 'will not be pushed around.' Very dishonest & weak".
The insult came in one of two blistering attacks by Trump's top aides for what they saw as Trudeau's betrayal of the president at the end of the weekend's G7 summit.
At the G7 summit Mrs May was holding formal face-to-face talks with all of the other leaders - except Mr Trump.
Trump also repeated an earlier proposal that US trading partners should drop all trade barriers, including tariffs and subsidies to industries and producers in their own countries. Trudeau stuck our president in the back.
At one point Kudlow, 70, referred to Canada's leader as "Pierre" Trudeau, confusing the prime minister with his late father, who served in the same capacity for more than 15 years between 1968 and 1984 and died in 2000.
"They fully understand where I am coming from".
"It may not be politically correct, but we have a world to run and the G7, which used to be the G8, they threw Russia out, they can let Russia come back in, because we should have Russia at the negotiating table", he said.
Trump cited progress on reaching an agreement on the North American Free Trade Agreement with Canada and Mexico, saying the final outcome would lead either to an improved trade deal or separate pacts with the two USA neighbors.