The NATO summit this week was a high stakes event for President Trump. NATO is a key component of the U.S.-led post-War international order that has made the world, on the whole, safer and more prosperous than in the past. Pax Americana — America's lone superpower status and web of security alliances and guarantees all around the world — deters great power conflict and enables global commerce to flourish. And yet, Trump seems determined to undermine NATO.