He tweeted again later Thursday night, complaining about the trade practices of the European Union and Canada.
The President's focus over the past weeks has been his June 12 summit with North Korean despot Kim Jong Un in Singapore and not the G7 meetings held with top US allies in a remote part of Quebec, people familiar with the preparations say. Trump has even questioned whether his presence is absolutely required in Canada.
It is, top advisers have responded, warning an absence at the premier meeting of top world leaders would amount to a retreat amid fierce clashes over economic and other issues. Trump has vented back that the meetings are unlikely to produce anything worthwhile, and that the trek to rural Quebec is a waste of time.
US allies have wondered and openly discussed how long Trump will remain at the G7 talks. Even as late as Thursday, some foreign officials -- based on conversations they have been having -- were still considering it a real possibility Trump could leave the summit early.
Aides have juggled how to fulfill the requirements of the G7 while at the same time preparing Trump for the high-stakes Singapore talks a few days later. Even before Thursday's announcement, the President was already planning to skip a working lunch with world leaders on Saturday focused on healthier oceans, people familiar with the matter said. Diplomats are likely to view the early departure as a way to avoid further animosity.
Trump alluded to the packed agenda in remarks from the Oval Office on Thursday.
"It will be a pretty crowded number of days. But very exciting and I think a lot of good results can come about," Trump said. He was optimistic about the Canada talks, saying he expected "some pretty good discussions" at the G7.
The schedule of meetings and photo-ops on the G7 agenda begins Friday with a family photo in the mid-afternoon. All the events are being held at a golf resort in rustic Charlevoix. The mood, according to nearly everyone involved, will be unpleasant.
Leaders are assembling at a fractured moment for US alliances after Trump slapped tariffs on steel and aluminum. His decisions to withdraw from the Paris climate accord and the Iran nuclear deal both came in the year since the last G7 meeting, held on a rocky cliffside in Sicily.
At that session, Trump felt cornered by leaders such as Macron, Trudeau and German Chancellor Angela Merkel, who tried to convey the importance of presenting a united front amid destabilizing threats like terrorism and climate change. Trump chafed at what he viewed as a lecture, according to aides, and left determined to plot his own path forward.
That's left Trump largely isolated among the other G7 nations, who have banded together in outrage.
The tariffs he imposed last week on Canada, Mexico and the European Union have drawn sharp backlash from allies, whose leaders have described feelings of anger, regret and confusion. Most have threatened retaliatory measures. But Trump's aides have signaled he's unwilling to rethink the decision.
"There are disagreements. He's sticking to his guns, and he's going to talk to them," said Larry Kudlow, Trump's top economic adviser, at a briefing on Wednesday. He described the disputes as a "family quarrel."
The session with Trudeau in particular promises to be chilly; the two men had a testy phone call at the end of May in which Trump inaccurately accused Canada of burning down the White House in the War of 1812 (it was actually the Brits).
Trump also had a "terrible" phone call with France's Macron around the same time, people familiar with the conversation said.
The wide disagreements have led to questions about whether the assembled leaders will produce the traditional "communiqué" that typically emerge from G7 summits. Merkel, predicting difficult discussions, has argued the leaders should not force a joint statement that waters down what the group has agreed to in the past. And Macron has insisted that any communiqué mention the Paris climate accord that Trump ditched last year.
"The will to have a text signed by 7 countries must not be stronger than the content of that text. On principle, we must not rule out a 6+1 agreement," Macron tweeted on Thursday.
Trudeau, as the summit's host, has placed climate and environmental issues atop his agenda, including a focus on ridding the world's oceans of plastic waste and making coastal communities more resilient to rising tides. A number of non-G7 leaders were invited to participate, including from Africa and island nations. The issue has gained significant attention over the past several weeks after a striking National Geographic cover showing a plastic bag submerged in the water like an iceberg.
Trump was initially expected to participate in a working session on the issue, but will no longer attend.
There was a back-and-forth inside the White House about curtailing the visit further, given the scheduling issues around the Singapore summit and Trump's steep differences with other G7 leaders. But it was determined that Trump's presence at the meetings would be critical, even as contentious interactions are expected.
Trump is flying directly to Singapore from the G7 and aides have been weighing the logistical challenges of the back-to-back summits.
Officials said earlier on Thursday that Trump may simply need to depart Canada earlier in order to make it to Singapore by Sunday evening. Kudlow, meanwhile, told reporters Wednesday that Trump is looking forward to the summit.
"The President wants to go on the trip," he said. "The President is at ease with all of these tough issues. He's proven himself to be a leader on the world stage. And he's achieved great successes, I might add, in foreign policy. So I don't think there's any issue there at all."