A former commander of U.S. nuclear forces is leading a call for taking U.S. and Russian nuclear missiles off high alert, arguing that keeping them less ready for prompt launch would reduce the risk of miscalculation in a crisis. It also could keep a possible cyberattack from starting a nuclear war, he said, although neither Washington nor Moscow appears interested in negotiating an agreement to end the practice of keeping nuclear missiles on high alert. Retired Gen. James Cartwright said in an interview that “de-alerting” nuclear arsenals could foil cyber intruders by reducing the chance of firing a weapon in...