The following month, visiting a U.S. military installation in Greenland with his wife, Mr. Vance had the temerity to attack Denmark on its own soil, complaining that the country was not doing enough “to keep our troops, and in my view, to keep the people of Greenland safe” from Russia and China. Twice last year, the Danish government summoned American diplomats over reports that the U.S. was spying and operating a covert influence campaign on its territory.