The G7 summit looked like it was going okay. Then Trump got mad on Twitter.

Just hours after leaving the G7 (Group of Seven) summit in Quebec on Saturday, President Donald Trump abruptly retracted US support for a joint statement signed by every nation in the group and blasted Canadian Prime Minister Justin Trudeau as “meek and mild.”

Firing off tweets aboard Air Force One, Trump said he was reversing the US position in response to Trudeau’s comments at a press conference at the end of the summit. Trudeau had pledged to impose tariffs on the US in response to Trump’s recent steel and aluminum tariffs against Canada.

“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,’” Trump tweeted. “Very dishonest & weak.”

Trump’s confrontational moves capped off two days of tense negotiations between the US and some of its most treasured allies. The annual meeting is typically marked by near consensus on issues like free trade.

Going into the summit, it was unclear if Trump was going to sign the customary joint statement in which the members of the G7, a club of some of the most powerful industrialized nations of the world, detail the policy positions and initiatives they agree on as the summit wraps.

A White House official told the Washington Post before the meeting that Trump was contemplating not signing the statement. The intent of this move would be to send a message that the US is perfectly happy to go its own way if the other members give it too much trouble during talks over issues like Trump’s controversial steel and aluminum tariffs.

In the end, Trump’s actions seemed significantly more petty. It appears that the president was behind signing the statement as he left the summit, but then decided to take it back because Trudeau pledged to follow through on earlier promises to retaliate against US tariffs at a press conference after he left.

There was nothing particularly surprising about Trudeau’s move — Canada had already threatened to issue tariffs, and retaliation over tariffs is common in the trade world. But it seemed to rub Trump the wrong way. Ultimately, Trump’s harshly worded tweets, personally insulting one of the US’s closest allies and overturning an apparent commitment made just hours earlier, made his exit from the summit even more acrimonious than most analysts expected.

During the summit, Trump’s meetings with leaders from the other G7 members — Canada, France, Germany, Italy, Japan, and the United Kingdom, plus the European Union (which is not technically part of the G7 but participates) — were reportedly pretty tense and confrontational.

That was to be expected. Trump has placed steel and aluminum tariffs on every other member of the G7, and that was bound to be a major topic of contention during talks. The French also intended to push Trump to make policy concessions on climate policy and the Iran nuclear deal.

The divides between the US and its allies were so big that France and Germany had signaled that they might refrain from signing the final joint statement unless the US made some major policy concessions.

Before everything wrapped up, it was hard to discern how the US would act. Trump’s comments to reporters before he left the summit sent mixed signals on where he stood. He said the complete elimination of tariffs was “the ultimate thing” that the countries were striving for. But he also said he would be willing to “stop trading” with countries that put unfair tariffs on US goods.

“We’re like the piggy bank that everybody’s robbing — and that ends,” he said.

Yet as the summit came to an end, it appeared that all the countries had decided to sign a final statement despite the tensions. Trudeau’s government released the joint statement and announced that it had been signed by all seven members of the G7.

But moments later, Trump blasted Trudeau and said the US was in fact not a signatory to the statement.

“Based on Justin’s false statements at his news conference, and the fact that Canada is charging massive Tariffs to our U.S. farmers, workers and companies, I have instructed our U.S. Reps not to endorse the Communique,” Trump tweeted.

Trump was responding to a press conference during which Trudeau had promised to retaliate against Trump’s tariffs with tariffs of his own.

“I have made it very clear to the president that it is not something we relish doing, but it is something that we absolutely will do,” Trudeau said. “As Canadians, we are polite, we’re reasonable, but also we will not be pushed around.”