President Donald Trump is pushing other countries within the NATO military alliance to contribute more to their defense spending — and the U.K.’s former defense minister has told CNBC that he agrees. “Half the alliance — 16 of the 29 countries — don’t even spend 1.5 percent (of gross domestic product) let alone 2 percent that we all agreed on four years ago (at a NATO summit) in Wales,” Michael Fallon, who served as secretary of state for defense from 2014 to 2017, said Tuesday.

“Four years on, and not enough European countries are making progress towards it and they need to do that and the president’s criticisms are quite valid.” Trump is due to attend a NATO summit in Brussels on Wednesday and the thorny issue of how much the alliance’s individual members spend on defense is certain to arise. On Tuesday, Trump was still tweeting his annoyance. Tweet Tweet

Number crunching

In 2014, NATO members agreed to target spending 2 percent of gross domestic product (GDP) on defense, although the contributions remain voluntary. In 2017, only the U.S., U.K., Greece, Poland and Estonia reached the 2 percent target. In 2017, the U.S. spent (at current exchange rates) an estimated $685.9 billion on defense, NATO data shows, the U.K. spent $55.3 billion and Germany $45 billion, compared to Canada’s $22.4 billion. The U.S. represented a 71.1 percent share of the alliance’s combined defense expenditure. NATO collects defense expenditure data from each member’s defense ministry. The latest data from the organization, released Tuesday, estimated that for 2018 the U.S. will spend 3.5 percent of GDP on defense, while NATO Europe and Canada are expected to both spend 1.47 percent.

Based on current prices and exchange rates. NATO

At a NATO summit in May 2017, Trump lambasted fellow member nations saying, "Twenty-three of the 28 member nations are still not paying what they should… Many of these nations owe massive amounts of money from past years." What makes Trump particularly cross is the fact that the U.S. pays so much “to protect Europe,” as Trump said last week at a rally in Montana, while Europe “kills us on trade” and the European Union had a 120 billion euro ($140 billion) trade surplus with the States in 2017 — a bone of contention for the president. Trump has since threatened that the U.S. might not come to the aid of a NATO member should it be attacked, and there are concerns that Washington. could pull troops out of Europe.

After several years of defense spending cutbacks, both France’s President Emmanuel Macron and German Chancellor Angela Merkel have pledged this year to increase defense spending — but both have signaled that the 2 percent target might not be reached for years. Berlin has only committed to 1.5 percent by 2024, but even NATO head Jens Stoltenberg has said that is not good enough. NATO is based on the principle of collective defense, meaning that an attack against one ally is considered an attack against all allies and, consequently, members will come to each other’s aid. But Trump has repeatedly said that the U.S. is paying way more than its fair share.

NATO Secretary-General Jens Stoltenberg addresses a news conference at the Alliance headquarters in Brussels, Belgium, March 15, 2018. Yves Herman | Reuters

The U.K.’s former defense minister said Trump’s position on defense was unlikely to have changed much from last summer. “Last year, when Trump came to the Brussels (NATO) summit, I recall how he was brand new and everyone wanted to meet him, everybody wanted to see how he would react. And he made some of the same points that he’s been making recently and he made them there — that Europe has to do more in its own defense.” With Trump heading to Helsinki, Finland, to meet Russian President Vladimir Putin next Monday, Fallon believed that NATO members would be keen to engage with Trump. “I think this time there will be more engagement with him. And not least because he’s going on from the summit to engage with President Putin and a lot of the members of NATO have a very strong interest in that, particularly Germany, but also those countries that border on to Russia.”

NATO ‘not a one-way street’

While the U.S. accounts for the most defense spending within NATO, the U.S. is a beneficiary from the alliance in more ways than one, strategists and military experts note. Hans Binnendijk, from the Center for Transatlantic Relations, and Magnus Nordenman, from the Atlantic Council think tank, concluded in a report entitled “NATO’s Value to the U.S.: By the Numbers” and published in April that the U.S.’ relationship “with its friends and allies is not a one-way street, where the United States makes, and the allies take.” They noted that the specified NATO commitment of 2 percent of GDP “is the most visible metric used to measure allied political commitment to burden-sharing across the alliance. However, that metric does not measure the output and quality of allied defense contributions. It says even less about how NATO relates to broader U.S. security and economic interests.”

U.S. Army soldiers from NATO at a checkpoint during a patrol against Islamic State militants at the Deh Bala district in the eastern province of Nangarhar Province. WAKIL KOHSAR/AFP/Getty Images

For instance, the writers noted: “France and the U.K. contribute about 30 percent of the total ballistic-missile-submarine deterrent fleet held by NATO members” and that “NATO countries also host sites for U.S. B-61 nuclear gravity bombs, and maintain dual-capable aircraft for nuclear delivery, which further enhance deterrence.” “NATO and its members contribute directly to U.S. national security through, among many other things, deterrence, deployments in support of U.S. operations, and forward basing close to key security hotspots,” the report said.