Vladimir Putin, Russia’s long-standing dictator, never got over the Soviet Union’s collapse at the end of the Cold War. He has called it the “greatest geopolitical catastrophe” of the 20th century and said he’d reverse it if he could. It’s starting to look as though Putin’s decades-old grudge might just pay off, as he sits on the sidelines and watches the United States do the work for him. The most powerful country in the world, which was — for good reason — Putin’s biggest nemesis until only two months ago, is now rolling out the red carpet for him, parroting...