Guard the Border Act This bill requires the Department of Defense (DOD) to reassign 95% of National Guard members deployed to the National Capital Region on or after January 6, 2021, in response to the attacks on the U.S. Capitol building and grounds. Specifically, DOD must reassign such members to support U.S. Customs and Border Protection in (1) securing the southern land border of the country, and (2) management and care for migrants at the border. DOD must report on the results of a study assessing the effects of such reassignment.