President Trump told North Atlantic Treaty Organisation allies on Wednesday he wants to see them spend four percent of their GDP on defense, doubling the now agreed-upon goal of two percent - a number most North Atlantic Treaty Organisation member states will fall well short of meeting for years to come.
Germany is extremely reliant on Russian gas, and the new Nord Stream 2 pipeline in the Baltic Sea, which Germany approved in March, will only increase its dependence.
Meanwhile, the Wall Street Journal reported Trump as saying "I'll do my own thing" if spending is not immediately increased.
"What they're doing is spending - at a much faster clip they're going up to the 2 percent level", Trump said.
In a face-to-face meeting with Chancellor Angela Merkel of Germany later in the day on the sideline of the summit meeting, Trump was more conciliatory, saying the two had a "very, very good relationship".
Before he visits with Putin, Trump will visit London and the United Kingdom - where many large protests are planned against his policies.
According to diplomats, he plunged the summit into chaos on Thursday by saying that the U.S. would "go it alone", if European states failed to boost their spending to at least 2% by January. They all made commitments and they will be up to 2%.
Not only did Trump demand on Twitter on Thursday that countries meet the 2% level by this year, not 2024, but he also said all countries should eventually hit 4%, which is more than even the United States now spends. Energy exports represent Russia's main source of revenue, and Trump argues that the pipeline undermines NATO's goal, as it's created to counter Russian aggression.
Asked about pressures on countries with weaker finances, he said, "We have many wealthy countries with us today but we have some that aren't so wealthy and they did ask me if they could buy the military equipment, and could I help them out, and we will help them out a little bit", he told a news conference.
Leaders of Azerbaijan and Georgia, non-NATO members, were asked to leave for the emergency session.
Trump claimed a personal victory at the summit after telling European allies to increase spending or lose Washington's support.
Senate Republican Conference Chairman John Thune, who also traveled to Russian Federation, said Trump should be prepared for complete denials and well-rehearsed answers when he meets with Putin in Finland's capital.
Merkel told reporters there followed a discussion with assurances to Trump that spending was increasing - something he later acknowledged was happening at an unprecedented rate.
Trump has said next week's meeting with Putin "may be the easiest" part of his European tour. "All I can do is say "Did you?' and 'Don't do it again" - but he may deny it".