Trump’s NATO Progress

President Trump will attend a summit of North Atlantic Treaty Organization national leaders this week, and the stakes are unusually high for everyone. He plans to meet Vladimir Putin shortly afterward, and Mr. Trump will be at a disadvantage if he doesn’t set the right tone in Brussels.

That tone should be a united front between America and its allies, within a NATO committed to and capable of deterring new threats. This doesn’t mean Washington must always avoid raising uncomfortable truths within the alliance. It does mean Mr. Trump should recognize how NATO benefits America, and how it can help him avoid the diplomatic traps into which his predecessor fell.

The good news is that Mr. Trump is doing better on this score than many of the pearl-clutchers among foreign-policy worthies will admit. He has taken a particularly aggressive stance on defense spending among NATO members, most recently in a series of testy letters reportedly sent to other national leaders. Allies have pledged to spend at least 2% of GDP, a promise they repeated at the 2014 Wales summit. Mr. Trump is continuing a long tradition of bipartisan frustration in Washington when they don’t meet that pledge.

But Mr. Trump should also give credit where it’s due, especially when he can claim part of the credit for success. Inflation-adjusted defense spending among non-U.S. NATO members has increased each year since 2014, and at an accelerating rate that likely will deliver the largest annual spending growth since the Cold War this year. More than half of NATO’s 29 members are on track to meet their 2% pledge by 2024, compared to four or five in a typical year before 2014. Mr. Trump’s win here is keeping up the pressure for more burden sharing as memories of Russia’s 2014 invasion of Crimea fade.

NATO also is making important progress on the capabilities that new money buys. Since 2015 the alliance has ramped up investment in a spearhead force capable of deploying up to 5,000 troops to trouble spots within 48 hours. Now the challenge is how to mobilize larger forces if needed, and Mr. Trump has an opportunity to lead real progress.

Defense ministers last month signed off on a new “four 30s” commitment—that by 2020 NATO Allies should be able to deploy 30 troop battalions, 30 air squadrons and 30 warships within 30 days. By encouraging his peers to give this plan their final endorsement, Mr. Trump can signal that the alliance is committed to being an effective deterrent.

Movements of troops across borders within NATO can still face considerable legal and bureaucratic obstacles, and cutting this red tape requires cooperation from defense ministries and interior ministries across Europe. In addition to his focus on spending, Mr. Trump could help America and the alliance by demanding firm commitments to fix this problem, perhaps with a deadline.

All of this would help Mr. Trump as he prepares to face off with Mr. Putin. The weakness in Mr. Trump’s NATO diplomacy so far, and it’s a big one, has been his willingness to denigrate the alliance, even to the point of suggesting America might withdraw from it.

Maybe that’s meant to scare other members into meeting their financial commitments, but when Mr. Putin hears the same comments they sound like a weak and fracturing West. His strategic goal is to crack the alliance so he can have a freer hand to dominate Eastern Europe and reassemble at least a de facto version of Greater Russia. He could then use his military leverage to influence diplomatic and economic decisions across Europe.

Mr. Putin snatched Crimea and invaded Ukraine because he learned over time that President Obama had no stomach for confrontation. Mr. Trump presumably isn’t eager to be humiliated in similar fashion. That is more likely to happen if he agrees to ease sanctions in return for Russian promises of good behavior, even as Mr. Putin concludes that NATO would struggle to respond to harassment of its eastern members.

Ronald Reagan knew better. His successful diplomacy with Moscow—which ended the Cold War—started with a strong commitment to Europe and friendly relations with Margaret Thatcher, Helmut Schmidt and then Helmut Kohl. His model of a willingness to negotiate, but only from a position of strength, can serve Mr. Trump well. A start will be to talk up, and expand on, NATO’s progress while renewing his commitment to the alliance.