Shortly after Russia’s unprovoked invasion, Putin put his military’s nuclear forces on high alert. Putin formally reduced the requirements for the Kremlin to deploy its nuclear weapons last year following Ukrainian attacks on the western Russian city of Kursk. That cleared the way for Russia to use nukes against any nation that attacks its territory and has the backing of a nuclear power. Recently, Trump has begun to sound more glum about the prospects of getting a deal done between the two sides. “Maybe it’s not possible to do,” Trump told NBC’s “Meet the Press” in an interview that aired...