In April 2018, U.S. Customs and Border Protection (CBP) leadership issued guidance that allowed officers to limit asylum seekers’ access to ports of entry. This guidance permitted CBP officers to be stationed at the United States’ international boundary with Mexico and inform arriving asylum seekers that U.S. ports of entry were full. Simultaneously, CBP officers also began accepting a specific number of asylum seekers each day, in a process that is known as metering. In June 2018, then-DHS Secretary Kirstjen Nielsen signed a memorandum that authorized port directors to begin metering at all U.S. ports of entry. As lines of asylum seekers grew in border cities, Mexican authorities and civil society groups responded by providing humanitarian assistance and creating informal waitlists. Since November 2018, the Robert Strauss Center for International Security and Law at the University of Texas at Austin—at times in collaboration with the Center for U.S.-Mexico Studies.