Conventional Prompt Global Strike and Long-Range Ballistic Missiles: Background and Issues [Updated February 14, 2020] [open pdf - 1MB]
From the Summary: "Conventional prompt global strike (CPGS) weapons may bolster U.S. efforts to deter and defeat adversaries by allowing the United States to attack high-value targets or 'fleeting targets' at the start of or during a conflict. Congress has generally supported the PGS [prompt global strike] mission, but restricted funding for several years. Recently, efforts to develop a long-range prompt strike capability, along with other efforts to develop extremely fast hypersonic weapons, have garnered increased support."
CRS Report for Congress, R41464
Congressional Research Service: https://crsreports.congress.gov/