Trump spent much of the day in meetings in Italy, demanding that the world's wealthiest nations to do more to fight terror while listening to their urgings about the need to stay in the Paris climate agreement.
And on trade, Trump was caught having stoked a contentious fire, as the German news magazine Der Spiegel reported the president had told leaders of the European Union before the summit began that the Germans were "bad" for having a large trade surplus with the United States.
From left to right, the President of the European Council Donald Tusk, Britain's Prime Minister Theresa May, US President Donald Trump, German Chancellor Angela Merkel, Japanese Prime Minister Shinzo Abe, Canadian Prime Minister Justin Trudeau, French President Emmanuel Macron, the President of the European Commission Jean-Claude Juncker and Italian Prime Minister Paolo Gentiloni pose after watching the Italian flying squadron.
As the G-7 summit got under way with four first-time attendees, Donald Trump chiefly among them, it remained unclear what position the US would take or even who would serve as Trump's top aide during the talks. British Prime Minister Theresa May was to lead a discussion on terrorism and issue a call for G7 countries to put more pressure on internet companies to ensure extremist content is quickly taken offline and notified to authorities.
John Kirton, director of the G7 Research Group at the University of Toronto, said the meetings are flawless for someone like Trump, who loves to be involved in making deals.
Transatlantic tensions on trade resurfaced after reports that Trump had described the Germans as "bad, very bad" and vowed to stop them selling millions of cars in the United States, during a meeting with senior European Union officials in Brussels on Thursday.
Italian officials have suggested it will be shorter than 10 pages, compared to 32 pages at the last G7 summit in Japan.
Italian Prime Minister Gentiloni said this declaration is also a strong message of solidarity to the United Kingdom after the Manchester attack.
Previous reporting has said other members of Trump's orbit are also focuses of the investigation, but the reports Thursday evening were the first to name a current White House official.
In Sicily, Trump was again received warily, a president who ran an "America First" campaign with suggestions of disentangling the United States from global pacts now engaged in two days of pomp and policy with the leaders of the United Kingdom, France, Germany, Italy, Japan and Canada.
"His views are evolving, he came here to learn", Cohn said.
The top issues of the two-day meeting Friday and Saturday are climate change, security, trade and immigration - and the differences between the leaders are substantial.
"We're always going to be clear at these meetings that climate change is a hugely important issue", Freeland said. One potential compromise that's emerged involves staying in the climate accord but adjusting the US emissions targets.
"We will bring the fight against terrorism to a higher level by relentlessly preventing, investigating and prosecuting terrorist acts, their perpetrators and supporters", said the text of a joint statement issued in the medieval Sicilian town of Taormina.
Abe and Trump met in person for the second time since Trump's inauguration in January. It was expelled from the group in 2014 following its annexation of Crimea from Ukraine.