Americans should be worried. The U.S. military has grounded all its new F-35 Joint Strike Fighters following an incident on June 23, when one of the high-tech warplanes caught fire on the runway of a Florida air base. The no-fly order — which affects at least 50 F-35s at training and test bases in Florida, Arizona, California and Maryland — began on the evening of July 3 and continued through July 11. To be fair, the Pentagon routinely grounds warplanes on a temporary basis following accidents and malfunctions to buy investigators time to identify problems and to give engineers time...