The White House is telling Congress that President Obama has the legal authority to continue American participation in the NATO-led air war in Libya, even though lawmakers have not authorized it. In a broader package of materials the Obama administration is sending to Congress on Wednesday defending its Libya policy, the White House, for the first time, offers lawmakers and the public an argument for why Mr. Obama has not been violating the War Powers Resolution since May 20. On that day, the Vietnam-era law’s 60-day deadline for terminating unauthorized hostilities appeared to pass. But the White House argued that...