"The problem is Trump seems to really see no benefit that allies provide the United States", says James Goldgeier, visiting senior fellow at the Council on Foreign Relations.
Trump tweets: "Why are their (sic) only 5 out of 29 countries that have met their commitment?"
Invited leaders from non-NATO countries Afghanistan and Georgia were asked to leave along with most North Atlantic Treaty Organisation leaders' retinues of officials, as the heads of state and government of the Western alliance sought to deal with the man whose nation commands much of the budget and forces for Europe's defence.
"Our President - the orange guy Trump- is in Belgium right now - at the NATO Summit, fighting over how many ways they will split the check", Jimmy Kimmel told his late night viewers about POTUS's latest.
But NATO chief Jens Stoltenberg pointed out that military spending had been rising in Europe since 2014 and members were making efforts to meet the objective, particularly Germany, which is often singled out by Trump for criticism.
Trump has made a big deal about money and demanded last night that allies meet the 2 percent threshold immediately, and not by 2024.
As for what he and Putin will discuss, Trump said Syria will be a main topic - as will Russia's attempts to interfere in the 2016 election that put Trump in the White House. In the afternoon, he heads to his next stop: the United Kingdom.
On day two, leaders will welcome non-NATO partners including Afghan President Ashraf Ghani and Ukraine's Petro Poroshenko to the alliance's new glass-and-steel headquarters as they seek to focus on policy rather than politics.
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What time will India vs England, 1st ODI match start? For India , the make-up of their playing XI will be their main concern. Expect much of the same from Kuldeep Yadav and Yuzvendra Chahal who wreacked havoc for England batsmen in the T20s.
The German Chancellor also addressed the accusation of Russian influence, saying "I have experienced myself how a part of Germany was controlled by the Soviet Union".
Others in the room, including the Lithuanian president whose country is among the most nervous of Russian ambitions, denied a suggestion that Trump had threatened to quit the alliance.
Trump, earlier, stated the opposite.
Trump has been more conciliatory behind the scenes, including at a leaders' dinner Wednesday. "I'm a very stable genius". The White House said that United States defense spending in 2017 was 3.6 percent of GDP.
Speaking to a cheering crowd at a rally this week, Trump told them that the U.S. would no longer be "the schmucks paying for the whole thing".
British Prime Minister Theresa May tried to set the tone on Wednesday by announcing more troops for NATO's Afghan training mission.
Nonetheless, he has simultaneously asserted that the USA should pay less. And one of the freedoms we have is freedom of speech and the freedom to express your views.
"We had a very intense summit", Merkel told reporters after the session.