NATO has upped its military spending since Donald Trump took the White House. While there are multiple reasons for the upswing, some of which predate Trump's presidency, defense experts say Trump's outspokenness on the issue has caused members to take their joint defense obligations more seriously.

NATO members are obliged to spend at least 2 percent of their country's GDP on security by 2024. When we first updated this promise — in March 2017, two month's into Trump's presidency — five countries met this requirement.

Last July, NATO Secretary-General Jens Stoltenberg said this number was expected to rise to eight in 2018. (NATO has not yet published complete spending data for last year.)

Stoltenberg credited Trump with focusing greater attention on the issue, saying "the upswing in NATO defense spending over the past year and a half demonstrates that his efforts are making a difference."

Spending by European members and Canada as a share of GDP has increased during Trump's presidency. In 2016, the year Trump was elected, the alliance's spending as a share of GDP was 1.42 percent. In 2017, it rose to 1.45 percent. It was projected to increase to 1.47 percent in 2018.

In terms of raw dollars, NATO members (excluding the United States) have spent more during this time period, from $286 billion in 2016, to $301 billion in 2017 to $312 billion in 2018.

But despite his claims to the contrary, Trump does not deserve the entire share of credit for the beefed-up military spending, defense experts said. Additional independent factors, like a NATO spending pledge that predates Trump's presidency and Russian revanchism in Ukraine, helped to pry open the coffers.

As of 2014, NATO's collective agreement directed members to spend 2 percent of their GDP on defense spending by 2024. That year also saw Russia annex Crimea.

Several defense experts we spoke to said these events set in motion the upward spending trend, which Trump has prodded along.

"Russia's threatening behavior has certainly played a role in inducing allies to increase defense spending," said Charles Kupchan, a senior fellow at the Council on Foreign Relations. "Have Trump's consistent complaints about European slackers also helped put pressure on allies to increase spending? Yes, he can credibly claim to have played a role. But he furthered a trend that was already in place."

Overall, Trump has asked countries to pay more for joint security, and some have made additional spending commitments. We rate this Promise Kept.

As president -- just as he did on the campaign trail -- Donald Trump has urged U.S. allies in NATO to pay more for their own defense.

Trump's musings about whether NATO -- the west's military alliance -- is "obsolete" have occasionally worried longtime allies. But Trump has a point that most NATO members are not complying with the alliance's target for military spending.

As of 2014, NATO's collective agreement directed members to spend 2 percent of their GDP on defense spending by 2024. According to NATO, only five counties meet that obligation today: the United States, Greece, Estonia, Poland and the United Kingdom.  

Since becoming president, Trump has done several things to jawbone NATO leaders to get their defense commitments up to the alliance's standard:

• On Feb. 5, Trump spoke with Jens Stoltenberg, the NATO secretary general, addressing, among other issues, "how to encourage all NATO allies to meet their defense spending commitments." Trump also said he would join a NATO leadership meeting in May 2017.

• On Feb. 6, Trump reiterated his call for enhanced defense spending during a visit to the United States Central Command at MacDill Air Force Base in Tampa. Saying that allies should "pay their fair share," Trump told an audience of military officials, "They're very unfair to us. We strongly support NATO, we only ask that all NATO members make their full and proper financial contribution to the NATO alliance, which many of them have not been doing."

• On March 17, Trump met with German Chancellor Angela Merkel and brought up the issue of NATO spending. The following day, Trump sent a pair of linked tweets that said in part, "Germany owes … vast sums of money to NATO & the United States must be paid more for the powerful, and very expensive, defense it provides to Germany!"

(We have previously noted the difference between maintaining the 2 percent of GDP spending threshold, which is a NATO requirement, and actually paying money to the United States for NATO, which is not.)

British Prime Minister Theresa May has said she has agreed to continue her efforts "to persuade my fellow European leaders to deliver on their commitment to spend 2 percent of GDP on defense, so that the burden is more fairly shared."

However, it's too soon to say whether he's been successful, because there is no indication yet whether the allies are putting more money into their militaries.

"While NATO members have hinted at the need for them bear more of the alliance's financial burden, there are also domestic political obstacles to them increasing their defense budgets that need to be overcome," said Matthew Fay, a defense and foreign policy analyst at the Niskanen Center.

Fay added that Trump is hardly the first president to pursue this goal -- it's been going on, he said, "for decades." To cite just one example, in June 2011, Robert Gates, then the defense secretary under President Barack Obama, criticized NATO for spending too little, saying that certain allies "are apparently unwilling to devote the necessary resources or make the necessary changes to be serious and capable partners in their own defense."

Based on these developments, it's clear that Trump has not given up on this promise. But until we see concrete evidence of additional spending commitments by NATO allies who are currently under the 2 percent threshold, we will rate this In the Works.