The audacious attacks on Russian airfields highlight the power of unconventional, asymmetric warfare — and the threat to U.S. strategic bases and ports, experts say.Ukraine’s surprise Sunday strike that used relatively inexpensive drones to knock out a significant portion of Russia’s long-range bomber capability was arguably the single largest blow to Moscow in its three-year war on its neighbor and a stunning display of asymmetric warfare. The out-of-the-blue drone blitz elicited glee among Ukraine’s backers in Washington, but also a chilling realization: The United States is increasingly vulnerable to just such a low-tech, low-cost strike. “The Pentagon should be very...