| Mexico was the single largest source of illegal migration during the 2021 fiscal year, as the Border Patrol arrested more than 608,000 Mexican nationals, according to unpublished U.S. Customs and Border Protection data obtained by The Washington Post. That leaves the Biden administration in an awkward position, as it increasingly relies on Mexico to tighten enforcement and block "caravan" groups heading north. An earlier alert mistakenly said the arrest totals were the highest since 1986. | 
