A terror weapon becomes less terrifying when it doesn’t work. After warning U.S. officials of its intention to launch, Russia lobbed a mysterious new ballistic missile—initially mistaken for a nuclear-capable ICBM—at the city of Dnipro in eastern Ukraine on the morning of Nov. 21, damaging buildings and injuring dozens of people. The mystery weapon turned out to be a variant of Russia’s RS-26, a 40-ton, solid-fueled missile with six independent reentry vehicles. Its name, Russian Pres. Vladimir Putin announced shortly after the strike, is “Oreshnik.” That’s Russian for “hazelnut tree.” Three months later on Thursday morning, the Russians reportedly launched...