At a World AIDS Day event last year honoring George W. Bush, the former President, wearing a suit and tie and a red solidarity ribbon, settled into a chair onstage, microphone in hand. “It takes a lot to get me back to Washington,” he said, “and PEPFAR is it.” Formally known as the President’s Emergency Plan for AIDS Relief, PEPFAR is easily one of the most successful foreign-policy initiatives in modern U.S. history. Created by Bush in 2003, at the height of the AIDS epidemic in Africa, the program is credited with saving as many as twenty-five million lives by investing in medicines and treatment networks. “I’m here to say as loud and clear as I can, Congress must fund PEPFAR,” Bush told his audience. “And you know what? It works, with verifiable results.”Funding PEPFAR has never been a...