Boeing’s 2707 was selected in 1966 as the U.S. entry in the supersonic-airliner race. Its design kept changing, including a shift away from a complex swing wing. NASA’s history records that Congress cancelled the national Supersonic Transport program in 1971 after roughly eight years of research and about $1 billion in spending. The 2707 never became a flying passenger plane. The future of travel arrived late, over budget, and not at all.
Sources: NASA, Supersonic Civil Aircraft: The Need for Speed; U.S. National Archives, “What Happened to the American SST?”.