President Barack Obama called NATO allies “free riders,” and President George W. Bush urged allies to “increase their defense investments,” both to little effect. But when Trump refused to immediately affirm that the United States would meet its Article 5 commitment to defend a NATO ally, NATO allies agreed to boost spending by $12 billion last year. That is a drop in the bucket: McKinsey calculated that allies need to spend $107 billion more each year to meet their commitments. Since polite pressure by his predecessors did not work, Trump is digging in on a harder line: On Thursday he suggested NATO members double their defense spending targets to 4 percent of GDP.

This is not a gift to Russia, as his critics have alleged. The last thing Putin wants is for Trump to succeed in getting NATO to spend more on defense. And if allies are concerned about getting tough with Russia, there is an easy way to do so: invest in the capabilities NATO needs to deter and defend against Russian aggression.