If Hillary Clinton is elected president, the world will remember Aug. 25 as the day she began the Second Cold War. In a speech last month nominally about Donald Trump, Clinton called Russian President Vladimir Putin the godfather of right-wing, extreme nationalism. To Kremlin-watchers, those were not random epithets. Two years earlier, in the most famous address of his career, Putin accused the West of backing an armed seizure of power in Ukraine by “extremists, nationalists, and right-wingers.” Clinton had not merely insulted Russia’s president: She had done so in his own words. Worse, they were words originally directed at...