Warplanes loyal to Gen. Khalifa Haftar shelled the Libyan capital’s only functioning airport, as the rogue military commander defied U.S. calls to halt an assault on Tripoli. Mr. Haftar, who opposes an internationally recognized government based in Tripoli, ordered the attack on the capital last week, a move that plunged Libya into one of its worst crises since the death of dictator Moammar Gadhafi in 2011. It has threatened to return the country to all-out civil war as forces allied to the Tripoli government raced to…