leaders in Brussels, and they will more warmly embrace the tough-talking American president.
The European Union is the top export market for the United States at $501 billion in goods and services in 2016, the latest available figures provided by the Office of the U.S. Trade Representative.
Mr Trump said: "The US is spending many times more than any other country in order to protect them".
Trump's weeklong trip to Europe will continue with a stop in Scotland before ending with a sit-down in Helsinki with Putin.
While countries closer to Russian Federation, such as Latvia, Lithuania, Romania, and Poland, significantly boosted defense, most other members took a more relaxed approach, with Germany's defense minister saying in 2015 that she didn't see a need to meet the spending bar, Deutsche Welle reported.
"In normal times, a president of the United States would rally the allies, develop a unified approach, and go with a strengthened hand to negotiations with the president of Russian Federation, rather than reducing his own leverage" former North Atlantic Treaty Organisation deputy secretary general Alexander Vershbow said to The Times.
Most NATO member states have not yet reached this goal, but a number of member states are expected to break the threshold in 2019.
"America does not have and will not have a better ally than Europe today", Tusk said. He can look to them for support when leaders get down to business Wednesday at the alliance's new headquarters.
"What's new is that this time, it's the president saying it and saying it very bluntly", Bromund said.
While defense spending has increased across the alliance, Trump says not enough has been done.
While some nations have taken that request (or demand) seriously and vowed to stick their hands deeper into their pockets, European Council President Donald Tusk cautioned the President: "it is always worth knowing who is your strategic friend and who is your strategic problem".
Last month, the president even wrote letters to a handful of European countries, urging them to up their defense commitments. We believe that the NATO alliance strengthens America because we speak with 29 voices to a Russian Federation that is one, to an Iran that is one, to a North Korea that is one. "Not fair to the US taxpayer".
In a brief question-and-answer session with reporters, he went farther.
Overall, NATO members will spend an average 2.40 percent of GDP on defense this year compared with 2.42 percent in 2017, the alliance said.
Under a 2014 agreement, each member state is required to boost military spending to 2 percent of its gross domestic product by 2024.
Four European members - Germany, France, Britain and Italy - combined pay 43.8 percent of the total. The six are Estonia at 2.14 percent, Greece at 2.27 percent, Latvia at 2 percent, Lithuania at 1.96 percent, Poland at 1.98 percent and the U.K.at 2.1 percent.