Two Russian strategic bombers conducted practice cruise missile attacks on the United States during a training mission last week that defense officials say appeared timed to the NATO summit in Wales. The Russian Tu-95 Bear bombers were tracked flying a route across the northern Atlantic near Iceland, Greenland, and Canada’s northeast. Analysis of the flight indicated the aircraft were conducting practice runs to a pre-determined “launch box”—an optimum point for firing nuclear-armed cruise missiles at U.S. targets, said defense officials familiar with intelligence reports. Disclosure of the nuclear bombing practice comes as a Russian general last week called for Moscow...