The meeting comes at a time of fraying relations across the European Union, so will anyone stand up to the US President? "Europeans spend on defense many times more than Russia and as much as China, and I think you can have no doubt, Mr. President, that this is an investment in common American and European defense and security, which cannot be said with confidence about Russian or Chinese spending".
At present, the United States of America is spending on defence much more than its European allies.
Before taking off on Air Force One, he tweeted: "Getting ready to leave for Europe".
Prior to departing the White House shortly after 7 a.m., Trump also fired off another tweet claiming credit for an economy that is "ROARING" and a Supreme Court nomination that he said has received "GREAT REVIEWS".
"This is why as part of our new budgetary proposals we, the Commission, have proposed to increase defense spending by 22 times, bringing total defense spending to Euro 27.5 billion [$32.2 billion] from 2021 to 2027", Juncker said.
As he left the White House to head for Brussels, where he is due to arrive late on July 10, Trump was asked by a reporter whether Putin is "a friend or foe". Speaking about solidarity, I want to dispel the American President's argument, which says that the USA alone protects Europe against our enemies, and that the U.S. is nearly alone in this struggle. I get along with her very well, I have a very good relationship. He has often railed against the US's key allies, accusing fueling trade deficits with the US. But we can not be taken advantage of.
European officials say while US defence spending makes up 70 percent of combined allied governments' military budgets, just 15 percent of USA expenditure is spent in Europe on NATO-related defence.
In 2014, North Atlantic Treaty Organisation countries with defense expenditure below 2 percent of their gross domestic product pledged to halt any decline in such outlays and "to move toward" that spending goal by 2024.
President Trump suggested such member states should reimburse the USA for being delinquent on their obligations for years. Four European members - Germany, France, Britain and Italy - combined pay 43.8 percent of the total.
"In the months ahead, we will step up our cooperation on military mobility, which is essential to our deterrence and defense".
'I've said that many times for many years. That includes running numerous military bases, missile defense systems, training operations, and more. "They are increasing defense spending because it's in their own security interest to do so".
The NATO summit is likely to be dominated by Trump's insistence that member nations step up and pay more for their joint defence.