The meeting brought together Mr Trump and Canada's prime minister Justin Trudeau, who irritated the U.S. president at the G7 by declaring that his country would not be pushed around.
As the European Commission announced a settlement with Gazprom on Monday (13 March), officials told EURACTIV.com it was "highly likely" that the executive will approve the controversial Nord Stream 2 pipeline project.
Trump has harshly criticized May, Merkel and Trudeau since taking office and opened Wednesday with another broadside against Merkel, asserting that her country is "totally controlled" and "captive" to Russia as he objected to a deal to bring Russian natural gas directly to Germany.
The two later had a bilateral meeting on the sidelines of the summit.
Baltic leaders, fearful of any repeat of Russia's annexation of Crimea, called for unity, while Slovak President Andre Kiska said his country was "one of the good guys" because it was increasing defence spending.
President Trump kicked off his trip to Europe with a biting critique of the United States' longtime allies, declaring at a breakfast meeting that Germany "is captive to Russian Federation".
"Explain that. And it can't be explained", Trump said.
German Chancellor Angela Merkel made a similarly dismissive response to Trump's statement, saying that her country "can make our independent policies and make independent decisions".
"The most likely outcome is the restarting of the strategic stability talks between the USA and Russian Federation", said Frank Rose, a former US assistant secretary of state for arms control now at the Brookings Institution think tank.
Referring to her own past living in the now defunct East Germany, Ms Merkel added: "I personally experienced how a part of Germany was controlled by the Soviet Union".
"We're supposed to be guarding against Russia and Germany goes out and pays billions and billions of dollars a year to Russia", Trump said in the presence of reporters at a pre-summit meeting at the residence of the United States ambassador to Belgium.
"President Trump should not meet with President Putin alone", Schumer ominously tweeted.
By slapping higher tariffs on European Union metals experts and threatening more on cars, Trump has shown his anger at the USA trade deficit with the European Union. "But other presidents never did anything about it because I don't think they'd up it or wanted to get involved", Trump said.
Trump used Germany as an example. Smith listed several ways that Germany has demonstrated friendship to the USA, including treating wounded American soldiers amid conflicts with terrorist groups.
"President Trump's brazen insults and denigration of one of America's most steadfast allies, Germany, is an embarrassment".
"Your message is having an impact, and we are going to build on that", Mr Stoltenberg told the U.S. president over toast and orange juice, before adding: "Let me also add that a strong North Atlantic Treaty Organisation is good for Europe and it's also good for the United States".
Bloomberg omitted the part where Radev said that Trump spoke first and added a claim from the Bulgarian leader that the USA president left the meeting immediately after his own remarks.
A joint declaration said: "We are committed to improving the balance of sharing the costs and responsibilities of alliance membership".