Over at The Hill, I endorse this week’s proposals from German and French leaders to create a pan-European army. The more American allies and friends take responsibility for their own affairs, the better for them—and for us. But I urge them not to launch into a project of this magnitude out of petty spite at President Trump’s manner or negotiating style. Founding a European force would be a huge and costly step. Europeans should undertake it for strategic reasons, not frivolous ones.