In a speech at the NATO summit on Thursday, Trump urged NATO countries to begin increasing their military spending. Several NATO leaders, including Angela Merkel, Justin Trudeau, Emmanuel Macron and Theresa May stood quietly and awkwardly as the President gave his criticism.

“NATO members must finally contribute their fair share,” he said. “Over the last eight years, the United States spent more on defense than all other NATO countries combined.”

So, is he right?

First, a bit of background. The North Atlantic Treaty Organization (NATO) is a collective security organization with 28 members. NATO developed during the Cold War as a bulwark against the Soviet Union(USSR) and today, remains the world’s strongest military alliance.

What defines NATO is the principle of collective security. Instead of having each member attempting to best their enemies’ military might, they pool together their resources and treat an attack on one member as an attack on every member. By pooling together military resources, each member pays less than they would if they were solely responsible for their defense.

Since it doesn’t have its own military, NATO relies on the militaries of its members. NATO members are advised to direct 2% of their GDP to military spending. The purpose of this is to ensure that no member is forced to contribute more than it has to.

Currently, only 5 of 28 of the NATO members pay their 2%. Trump argues that this forces the USA to spend more on its military, to make up for other members’ shortcomings. He would say that other countries spend less on their militaries because they know the US will come to their defense. Former President Barack Obama had similar concerns.

“I want to take this opportunity to commend Greece for being one of the five NATO allies that spends 2 percent of GDP on defense, a goal that we have consistently set but not everybody has met,” Obama said. “Greece has done this even during difficult economic times. If Greece can meet this NATO commitment, all our NATO allies should be able to do so.”

Trump’s concerns about NATO members’ defense spending are real. In order to portray a united, strong and committed front to NATO’s enemies, all NATO members must buy in. Trump’s grievances about the USA paying for other members’ shortcomings are also somewhat justified. Then again, Trump and the Republicans will probably support increases to military spending regardless.

Trump has made this a cornerstone of his foreign policy and probably unjustifiably so. It seems as though NATO members have already got the message. Excluding the USA, NATO members increased their military spending by 3.8% in 2016. In the past, Trump has even conditioned the USA’s commitment to Article 5 of NATO’s charter on members’ abilities to “fulfill their obligations” to the USA. Article 5 is the glue that keeps NATO together; it’s too important for the President to forgo for the sake of fairness to the USA.

Trump also failed to mention Article 5 in his speech to NATO leaders. For a president under investigation for possible ties to Russia, reaffirming the importance of article 5 to nervous world leaders would have been a wise move, especially if Trump is as innocent as he says he is.