National Commission on U.S. Counterterrorism Policy Act of 2020 This bill establishes within the legislative branch the National Commission on U.S. Counterterrorism Policy to review U.S. counterterrorism objectives, priorities, capabilities, policies, programs, and activities, and assess how to adapt and prioritize them. The commission shall study, among other things the evolution of threats to the United States from September 11, 2001, from international and domestic terrorism, major lessons learned from U.S. counterterrorism activities since that date, potential new or emerging challenges of conducting counterterrorism operations in contested environments, and recommendations on how best to adapt U.S. counterterrorism activities to address existing and emerging terrorism risks.