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.