WASHINGTON—President Donald Trump said on May 19 that when finished, his planned White House ballroom will be the “safest building ever built” and will serve both as a ceremonial venue and as a military-grade facility to help protect the nation’s capital. Speaking to reporters about the project’s construction progress, Trump said the structure would be designed to withstand both drone and missile attacks, with “a massive drone capacity.” He said the building will also have a drone port on the roof to help protect all of Washington. The structure will feature a hospital, research facilities, meeting rooms, and dedicated spaces for military personnel....