Mr. Putin was now gaining considerable traction by casting himself as a reliable friend and trading partner to Europe even as the Trump administration was treating its closest allies there as strategic and economic competitors…

Though careful not to gloat, Mr. Putin had to take great satisfaction in the recent turn of events. Often dismissed as a tactician and opportunist, he was looking more like a grand strategist as Mr. Trump bluntly rejected European demands for an exemption from what Brussels considers illegal and unilateral tariffs on steel and aluminum.

Populist, Russophile parties are in power in Greece, Hungary, Italy and Austria. The prospect of attaining Mr. Putin’s immediate goal of throwing off economic sanctions imposed by the European Union over the last several years suddenly seemed within reach, even without compromise in Ukraine.