Trump's comment - a tongue-in-cheek admission of an unspoken truth hanging over the June 15-17 summit of the Group of Seven powers in the French resort of Evian-les-Bains - followed a joint leaders' statement that could bolster Kyiv's growing leverage in potential peace talks with Moscow.
Ukrainian President Volodymyr Zelenskiy and his allies came to the G7 hoping to impress upon Trump that Ukraine's fightback is delivering results, and that Russia is in no position to be dictating terms for any peace deal.
The joint statement and comments from leaders suggest Trump has warmed to Zelenskiy's argument after years of scepticism.
However, any hopes of strongarming Moscow into peace talks still rely on Trump commitments, which can be elusive.
It was unclear if bilateral Trump-Zelenskiy talks would take place, and it also remains to be seen if Washington will allow waivers to lapse on sanctions restricting Russian oil exports, now that he has secured a preliminary Iran deal.
"I'm the boss," Trump told G7 chiefs and reporters on Wednesday as he arrived to take his seat at a session on global economic security, where leaders were due to discuss supply chains for critical minerals and macroeconomic imbalances.
Trump on Tuesday heralded a "very good" meeting with Zelenskiy and other G7 leaders.
"There has been a change in position on the part of the United States and President Trump," Canadian Prime Minister Mark Carney told reporters.
"There is a position that is harder toward Russia and more realistic, in our view, of the situation on the ground of the war."
G7 chiefs also welcomed the preliminary peace deal between the United States and Iran - which Trump signed on the eve of the summit - and said they were ready to contribute to its implementation.
They said they would make efforts to diversify energy supply routes to reduce dependence on the Strait of Hormuz, which Iran has blocked for most of the duration of its war with the US, and increase stocks.
France is now pushing partners to sign a joint statement on critical minerals that could include measures to help the West reduce its reliance on China and shield investors from countermeasures and dumping, diplomats said.
China spooked the global economy in 2025 when some industries nearly ground to a halt after Beijing imposed export curbs on permanent magnets made of rare earths.
"We are negotiating texts that are significant on critical minerals and, as a consequence, on economic sovereignty," a French presidency official said before the summit.
Measures under discussion in recent months have included price supports, market standards, subsidies and guaranteed purchases, as well as ways to scale up private investment in critical mineral supply chains outside China.
G7 leaders were also due to discuss how to rebalance global trade and address "predatory competition", mainly from China.
France summarises the imbalances as: "China produces too much, the US consumes too much and the Europeans invest too little."
Alarm is growing in Europe at China's trade surplus and its move up the value chain, in what analysts describe as a "second China shock" following its dominance of low-value industries in the 2000s.
Beijing rejects EU claims of unfair subsidies and has repeatedly vowed "strong" countermeasures to the EU's proposed "Buy European" and revised tech sovereignty rules.
G7 leaders were also due to discuss AI on Wednesday, with OpenAI founder Sam Altman and Anthropic CEO Dario Amodei expected to attend.
