Trump's relations with the others have hit such a low point that it was uncertain whether the seven countries can agree on a joint statement of priorities at the conclusion of the meeting.
Trump also defended his recent imposition of punishing steel and aluminum tariffs was based on legitimate national security concerns, and said he stood firm against the concerns of his fellow G7 leaders during their talks. "Take down your tariffs & barriers or we will more than match you!"
"The EU understands that the only way with Trump is strength", said one European official.
His economic adviser Larry Kudlow backed up the call, saying, "We're going to clean up the global trade system".
The two-day summit here was meant to cool tensions between Trump and other world leaders, but as they departed on Saturday it became clear that many are still searching for answers and also searching for ways to deal with the unpredictable US leader. "It is going to stop or we are going to stop trading with them".
Mr Trump earlier warned his counterparts against retaliation after the USA imposed tariffs on steel and aluminium from Europe, Mexico and Canada - saying they would be "making a mistake".
"They do so much more business with us than we do with them. the numbers are so astronomically against them ... we win that war a thousand times out of a thousand".
But by summer 2018, numerous staff and appointees who were supposed to keep things on track, keep the president contained, and whose presence was specifically cited by the U.S. Congressional delegation at the 2018 Munich Security Conference as proof that "all is well" are gone.
That leaves Trump diametrically opposed with Canada, which says renegotiating the deal every five years would create perpetual uncertainty and harm long-term investment.
G7 participants were also angered by Trump's stance on climate climate - a key issue on the group's agenda.
The whole interaction was not as long as the epic 25-second handshake when Trump visited Paris last Bastille Day when it appeared that Trump simply would not let go. "Whether you like it or not ... we have a world to run".
In an "extraordinary" exchange, Mr Trump repeated a list of grievances about United States trade - mainly with the European Union and Canada, a French presidency official said.
German Chancellor Angela Merkel said earlier that Russia's return to the club was out of the question.
When a CNN reporter asked Trump about anger and frustration from U.S. allies over trade, he lambasted the reporter and his "fake friends at CNN". "He's my friend, we have had a great relationship from the very beginning". Many reporters "are unbelievably dishonest".