All this was before Mr. Trump announced last weekend that he would impose tariffs by presidential fiat on some of our closest allies if they didn’t surrender to his hunger for Greenland. He eventually retreated from both tariff and invasion threats after his beloved stock market fell sharply. But unilaterally undermining the alliance that has kept our country safe for more than three-quarters of a century was strategic lunacy and showed how much wreckage one man can leave behind when he’s allowed to cast aside all constraints on his appetites.