The summit is set to address issues related to Nato's future and will make important decisions in that regard. Such considerations, he outlined on Twitter.
Macron - who at 40 is young enough to be Trump's son - was the first foreign leader treated to a lavish state visit to Washington.
Derek Chollet, executive vice president of the German Marshall Fund of the United States, a think tank, says there is a clear connection between Trump's criticism of German defense spending and reports that the Pentagon has undertaken a review of the cost of keeping troops in Europe.
Brussels and ebroidery harshly criticized the trade war of the United States of America against other countries, and on June 22 entered into force on penalty duties on European Union goods, a number of U.S. in the amount of €2.8 billion per year.
Trump pressed on: "If you look at it, Germany is a captive of Russian Federation, because they supply -- they got rid of their coal plants, got rid of their nuclear, they're getting so much of the oil and gas from Russian Federation".
Trump had said before leaving Washington that his meeting in Helsinki with Russian President Vladimir Putin next Monday "may be the easiest" part of his upcoming European tour, which also includes a trip to Britain, where the government is in crisis over Brexit.
He will also visit the United Kingdom at a time when the government of Prime Minister Theresa May faces another political crisis following the resignation of two of her principal ministers, both critics of her Brexit plan to negotiate a smooth withdrawal from the European Union.
"Dear America, appreciate your allies, after all you don't have all that many", he said.
Under fire for his warm embrace of Russia's Vladimir Putin, Trump on Wednesday also turned a harsh spotlight on Germany's own ties to Russian Federation, alleging that a natural gas pipeline venture with Moscow has left Merkel's government "totally controlled" and "captive" to Russian Federation.
Merkel and Trump have had a rocky relationship since the early days of his presidential campaign, when he claimed she was "ruining Germany" after Time Magazine picked her as the 2015 Person of the Year instead of him.
Last month, he said that Trump's politics had put trans-Atlantic relations "under tremendous pressure" and warned Europeans to prepare for darker times.
The ties between the US and many of its longest-standing allies have frayed since Trump took office and put his "America first" agenda into practice.
But the next morning, the bad guy persona was back, prompting the first formal North Atlantic Treaty Organisation crisis meeting since 2008 in which Trump aired his grievances in a leaders-only, unscripted session over the funding issue again, diplomats said.
As per The Hill, President Trump has attacked EU ahead of the summit, while alleging that the Europeans have taken advantage of the US on trade issues while failing to invest enough into their own defense for years. "Who would think? Who would think?"
"Disparaging long-standing allies at the same time as talking up the country that has wantonly seized territory and redrawn Europe's borders by military force for the first time since World War Two is disconcerting to say the least", said Boudreau.
Taking numerous questions from the global press corps, Trump offered a preview of his meeting Monday with Russian President Vladimir Putin, who he described as "a competitor". In effect, they have turned the tables on the US president, taking the thorny issue of money out of the equation and testing Trump's commitment to European stability itself.
"Germany owes a lot to NATO", Merkel added.
"I don't think that's helping Russian Federation", he said.
Might a reordering, or even a reduction, of USA forces in Europe be in the cards?
Germany's Defense Minister Ursula von der Leyen responded more directly to the Nord Stream criticism in a BBC interview at the summit: "We can cope with it".
Britain's summer 2016 referendum saw the leave side prevail by a 52-48 margin - a populist victory combined with Trump's surprise victory in the US presidential race later in the year that sparked upheaval in the global order.
At NATO, Trump did not specify which countries had committed to what, and it remained unclear whether any had changed their plans.
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