	Introduction

In recent years, Central American migrant families have been arriving at the U.S.-Mexico border in relatively large numbers, many seeking asylum. While some request asylum at U.S. ports of entry, others do so after attempting to enter the United States illegally between U.S. ports of entry. On May 7, 2018, then-Attorney General Jeff Sessions announced that the Department of Justice (DOJ) implemented a "zero tolerance" policy toward illegal border crossing, both to discourage illegal migration into the United States and to reduce the burden of processing asylum claims that Administration officials contend are often fraudulent. Under the zero tolerance policy, DOJ prosecuted 100% of adult aliens apprehended crossing the border illegally, making no exceptions for whether they were asylum seekers or accompanied by minor children. DOJ's "100% prosecution" policy represented a change in the level of enforcement of an existing statute rather than a change in statute or regulation. Illegal border crossers who are prosecuted by DOJ are detained in federal criminal facilities. Because children are not permitted in criminal detention facilities with adults, detaining adults who crossed illegally requires that any minor children under age 18 accompanying them be treated as unaccompanied alien children (UAC) and transferred to the care and custody of the Department of Health and Human Services' (HHS's) Office of Refugee Resettlement (ORR). The widely publicized family separations were therefore a consequence of the Administration's policy of 100% prosecution of illegal border crossing, and not the result of a direct policy or law mandating family separation. Since the policy was implemented, "under 3,000" children may have been separated from their parents, including at least 100 under age 5. The Trump Administration and immigration enforcement advocates maintain that the zero tolerance policy was necessary to dis-incentivize migrants from coming to the United States and clogging immigration courts with fraudulent requests for asylum. Immigrant advocates contend that migrant families are fleeing legitimate threats of violence and that family separations resulting from the zero tolerance policy were cruel and violated fundamental human rights. It explains enforcement policies under past Administrations and then discusses the Trump Administration's zero tolerance policy on illegal border crossers and the attendant family separations. Aliens who wish to request asylum may do so at a U.S. port of entry before an officer with the Department of Homeland Security (DHS) Customs and Border Protection (CBP) Office of Field Operations or upon apprehension between U.S. ports of entry before an agent with CBP's U.S. Border Patrol. Such individuals are placed in the custody of the U.S. All children are detained according to broad guidelines established through a court settlement agreement (applicable to all alien children) and two statutes (applicable only to unaccompanied alien children). Finally, the William Wilberforce Trafficking Victims Protection Reauthorization Act of 2008 (TVPRA) directed DHS to ensure that all UAC be screened by DHS for possible human trafficking. As a result of a 2015 judicial interpretation of the Flores Settlement Agreement, children accompanying apprehended adults cannot be held in family immigration detention with their parents for more than 20 days, on average. Consequently, if a family unit was apprehended crossing illegally between ports of entry, the zero tolerance policy mandated that CBP refer all illegal adult entrants to DOJ for criminal prosecution. On June 20, 2018, following considerable and largely negative public attention to family separations stemming from the zero tolerance policy, President Trump issued an executive order (EO) mandating that DHS maintain custody of alien families "during the pendency of any criminal improper entry or immigration proceedings involving their member," to the extent permitted by law and appropriations. DOJ continued to maintain that its zero tolerance policy was in effect. Some immigration observers question the Administration's ability to marshal resources required to prosecute all illegal border crossers given that Congress has not appropriated additional funding to support the zero tolerance policy. Some in Congress have criticized the family separation policy because of its cost in light of alternative options, such as community-based detention programs. Trends in Alien Apprehensions

Increasing numbers of apprehensions of Central American families and children are occurring within the context of relatively low historical levels of total alien apprehensions ( Figure A-1 ). However, in the first four months of FY2019, family units and unaccompanied children comprised roughly 60% of all apprehended aliens. CBP data on family unit apprehensions at the Southwest border are publicly available starting in FY2012, when they numbered just over 11,000.
For the last several years, Central American migrant families have arrived at the U.S.-Mexico border in relatively large numbers, many seeking asylum. While some request asylum at U.S. ports of entry, others do so after entering the United States "without inspection" (i.e., illegally) between U.S. ports of entry. On May 7, 2018, the Department of Justice (DOJ) implemented a "zero tolerance" policy toward illegal border crossing both to discourage illegal migration into the United States and to reduce the burden of processing asylum claims that Administration officials contend are often fraudulent.
Under the zero tolerance policy, DOJ prosecuted all adult aliens apprehended crossing the border illegally, with no exception for asylum seekers or those with minor children. DOJ's policy represented a change in the level of enforcement of an existing statute rather than a change in statute or regulation. Prior Administrations prosecuted illegal border crossings relatively infrequently.
Criminally prosecuting adults for illegal border crossing requires detaining them in federal criminal facilities where children are not permitted. While DOJ and the Department of Homeland Security (DHS) have broad statutory authority to detain adult aliens, children must be detained according to guidelines established in the Flores Settlement Agreement (FSA), the Homeland Security Act of 2002, and the Trafficking Victims Protection Reauthorization Act of 2008. A 2015 judicial ruling held that children remain in family immigration detention for no more than 20 days. If parents cannot be released with them, children are treated as unaccompanied alien children and transferred to the Department of Health and Human Services' (HHS's) Office of Refugee Resettlement (ORR) for care and custody.
The widely publicized family separations were a consequence of the Trump Administration's zero tolerance policy, not the result of an explicit family separation policy. Since the zero tolerance policy was implemented, up to 3,000 children may have been separated from their parents. In addition, thousands more were separated prior to the public announcement of the policy change.
Following mostly critical public reaction, President Trump issued an executive order on June 20, 2018, mandating that DHS maintain custody of alien families during the pendency of any criminal trial or immigration proceedings. DHS Customs and Border Protection (CBP) subsequently stopped referring most illegal border crossers to DOJ for criminal prosecution. A federal judge then mandated that all separated children be promptly reunited with their families. Another rejected DOJ's request to modify the FSA to extend the 20-day child detention guideline. DHS has since reverted to some prior immigration enforcement policies, and family separations continue to occur based upon DHS enforcement protocols in place prior to the 2018 zero tolerance policy.
Administration officials and immigration enforcement advocates argue that measures like the zero tolerance policy are necessary to discourage migrants from coming to the United States and submitting fraudulent asylum requests. They maintain that alien family separation resulting from the prosecution of illegal border crossers mirrors that which occurs regularly under the U.S. criminal justice system policy where adults with custody of minor children are charged with a crime and may be held in jail, effectively separating them from their children.
Immigrant advocates contend that migrant families are fleeing legitimate threats from countries with exceptionally high rates of gang violence, and that family separations resulting from the zero tolerance policy are cruel and violate fundamental human rights—such as the ability to request asylum. They maintain that the zero tolerance policy was hastily implemented and lacked planning for family reunification following criminal prosecutions. Some observers question the Trump Administration's capacity to marshal sufficient resources to prosecute all illegal border crossers without additional resources. Others criticize the family separation policy in light of less expensive alternatives to detention.
In prior years, most individuals apprehended were single adult males. Family unit apprehensions, which increased from just over 11,000 in FY2012 to 99,901 in the first four months of FY2019, and apprehensions of unaccompanied alien children are occurring within the context of otherwise relatively low historical levels of total alien apprehensions. In addition, the national origin of recently apprehended family units and unaccompanied children has shifted to mostly Central American from long-term trends of mostly Mexican.