Indeed, Johnson said he would tell Trump to pull back from a trade war that is already destabilising economic growth around the world. Press secretary Stephanie Grisham issued a statement saying the press had "greatly misinterpreted" Trump's comments.
On Friday, Mr Trump responded to a new hike in Chinese tariffs on United States goods by imposing heavy extra levies against a total of US$550 billion (S$760 billion) in Chinese imports.
White House economic adviser Larry Kudlow, who was in the room when Trump spoke and was later interviewed by CBS' "Face the Nation", offered his own explanation.
"The president was asked if he had "any second thought on escalating the trade war with China". Might as well. I have second thoughts about everything".
"We're going to be significantly expanding our trading relationship when the USMCA gets done and completed", Trump said alongside Trudeau.
"Yeah, sure, why not", Trump admitted, but quickly added that he has "second thoughts about everything".
Trump's decision came hours after China imposed an additional 10 percent of tariffs on about $75 billion on goods from the United States.
Trump has tried to downplay concerns the meetings of the Group of Seven leaders are strained, saying in a tweet that the leaders are all "getting along very well", and taking issue with some media reports indicating otherwise.
"Just to register a faint, sheep-like note of our view on the trade war - we are in favour of trade peace on the whole", Johnson told Trump.
"We are searching for ways Europe can in fact implement its commitments so that we can reverse the steps we have taken", he said. I mean, it doesn't matter; you can write whatever you want to write.
Boris Johnson's Brexit backstop bid rejected by European Union leaders
Merkel said the backstop was intended only as a transitional rule for the not finally resolved Ireland issue. A French presidential aide added that a no-deal Brexit was fast becoming the most likely scenario.
Trump then entered the first official summit meeting, initially set as a discussion of foreign policy and security issues.
A White House official added no United States officials met with Mr Zarif during the visit.
One of the Iranian officials also said Iran's ballistic missile program was not open for negotiation. Trump has imposed or threatened to impose tariffs on all three markets in his pursuit of free, fair and reciprocal trade.
Two U.S. officials said the Trump delegation was also irked that Macron had skewed the focus of the G7 meeting to "niche issues" at the expense of the global economy, which many leaders worry is slowing sharply and at risk of slipping into recession.
French President Emmanuel Macron, as current president of the G7, will hold talks with Iranian authorities to find a way to save the 2015 nuclear accord, a French presidential source said Sunday.
German Chancellor Angela Merkel disagreed, with her office saying Saturday that blocking the deal with the South American trade bloc, Mercosur, won't reduce the destruction of rainforest in Brazil, although she backed Macron's proposal to discuss the fires at the summit.
Trump disputed that he had signed off on any such message.
Macron has over the last months sought to play the prime mediation role between the West and Iran after US President Donald Trump previous year walked out of the 2015 nuclear deal and Iran ramped up its atomic activities.
Trump said he had a "fantastic lunch" with Macron on Saturday in Biarritz, France, which is hosting the gathering of world leaders.
French officials have said that Trump's "maximum pressure" approach to Iran is doomed to fail. It was unclear if anyone from the Iranian delegation would meet with Trump or US officials at the summit.