WASHINGTON—China, in the midst of a rapid nuclear weapons buildup, will soon surpass Russia as the United States’ top nuclear threat, a senior U.S. military official said on Friday, warning that the two countries have no mechanisms to avert miscommunication. U.S. Air Force Lieutenant General Thomas Bussiere, the deputy commander of the U.S. Strategic Command, which oversees the country’s nuclear arsenal, said China’s development of nuclear capabilities “can no longer be aligned” with its public claim that it wants to maintain a minimum nuclear deterrent. “There’s going to be a point, a crossover point, where the number of threats presented by China will exceed the number of threats that currently Russia presents,” Bussiere told an online forum. He said the determination would not be based solely on the number of Beijing’s stockpiled nuclear warheads, but also on how they are “operationally fielded.” “There will be a crossover point, we believe, …