"Greek Parade Paris 1919" by D. Vassiliou is a public domain image, via Wikimedia Commons

Donald Trump wants a military parade down Pennsylvania Avenue. He went to Paris last year and watched the Bastille Day parade on the Champs-Élysées with Emmanuel Macron, and now, like any toddler, he wants one of his own.

Never mind that nearly everyone with any authority on the subject thinks it’s a bad idea, including many within the Pentagon itself. Never mind that it will take away equipment and trai...