Strengthening the Posse Comitatus Act of 2020 This bill modifies provisions of the Posse Comitatus Act that prohibit the willful use of any part of the Army or Air Force to execute the law unless expressly authorized by the Constitution or an act of Congress. Specifically, the bill expands the applicability of the Posse Comitatus Act to all branches of the Armed Forces. The bill also prohibits the use of evidence obtained by or with the assistance of a member of the Armed Forces in violation of the bill.