The U.S. electric grid has become increasingly vulnerable to what the federal government is describing as an unprecedented wave of attacks that threatens to cripple the nation, according to a new investigative report that warns the energy industry is lagging in efforts to boost physical security of these critical sites. Amid a wave of increasing attacks across the country on key power stations, the North American Electric Reliability Corporation, or NERC, has been struggling to force the power industry to enact a series of security improvements meant to stop would-be attackers and terrorists from crippling the nation's infrastructure. Since 2014,...