President Donald J. Trump is using every tool imaginable to decrease the number of immigrants in the United States. Some of his tactics, such as reducing the number of refugees eligible for admission, are within his sole discretion. Others, like “constructing a border wall and ensuring the swift removal of unlawful entrants,” require cooperation with other branches of government, which is not Mr. Trump’s strong suit. We recently suffered a partial federal government shutdown (and may do so again) because authorization for federal spending ran out in December and Congress has not acceded to Mr. Trump’s demand to include spending for a southern border wall in legislation to fund the government.

Meanwhile, our diplomatic relations are in turmoil. Nevertheless, international cooperation is needed if Mr. Trump is to achieve his deportation goals.

Regardless of the law under which a person is deported, everyone who leaves (or is not permitted to enter) the United States must go somewhere.

Deportation is a catchall phrase. It includes the formal removal process guaranteed by statute to those who entered legally but have been convicted of certain crimes or accused of violating their immigration status, as well as the “swift removal of unlawful entrants” through an expedited removal process. Expedited removal currently is applied to migrants who entered without authorization and were apprehended within two weeks of their arrival and within 100 miles from the U.S. border. It also is used to deny entry to “arriving aliens” who dare to apply for admission (and usually asylum) without the required documentation. Removal has long-lasting consequences; every alien who is removed, whether expeditiously or not, is barred from admission to the U.S. for a certain period of time—five years after an expedited removal, 10 years after formal removal, and 20 years after a second removal or conviction for an aggravated felony. With permission, migrants can avoid these time bars by withdrawing their applications, immediately and voluntarily returning to their homelands, or agreeing to voluntary departure. In 2018, the Trump administration enticed parents to accept voluntary departure as a means to be reunited with their separated children.

Regardless of the law under which a person is deported, everyone who leaves (or is not permitted to enter) the United States must go somewhere. Mr. Trump cannot unilaterally remove people from the United States because they must be removed to other nations, and those nations must give permission for returning nationals or migrants from other countries to cross their borders. This can be problematic for numerous reasons, including a lack of documentation or a lack of citizenship (statelessness). (The United Nations estimates 10 million people have no citizenship.) Even when citizenship can be established, countries may put restrictions on the return of migrants.

In 2008, for example, the United States and Vietnam entered into an agreement for the “orderly and safe” repatriation of Vietnamese citizens who violated U.S. law and met other specified criteria, but Article 2, Section 2 of the agreement exempted Vietnamese citizens who “arrived in the United States before July 12, 1995, the date on which diplomatic relations were re-established between the U.S. Government and the Vietnamese Government.” In 2017 the Trump administration unilaterally determined this exemption did not apply to convicted criminals. Although a few Vietnamese were deported under this policy, the United States was forced to suspend it when Vietnam stopped issuing the required travel documents. Recent reports indicate the Trump administration is now negotiating with the Vietnamese government to deport more Vietnamese citizens who arrived in the United States before the restoration of diplomatic relations.

Depending on cooperation from Mexico

The need for coordination with other governments is most obvious at the U.S.-Mexico border. In 2016, the United States and Mexico entered into nine separate agreements regarding the organized repatriation of Mexican citizens. The agreements include notification requirements regarding, among other things, the identity, criminal activity (if any) and urgent medical needs of returnees. The time, place and number of Mexican citizens who can be returned on any given day are specified, and the agreements obligate the United States to protect the legal rights of unaccompanied minors and lawfully process their valid asylum claims and claims to be victims of “severe” human trafficking:

DHS personnel must determine whether an unaccompanied child encountered at a land border or port of entry is capable of making an independent decision [concerning an application for admission] and screen appropriately for signs [of] victimization of a severe form of trafficking, risk of trafficking upon return, and fear of return due to a credible fear of persecution.

Despite these agreements and the close cooperation needed with the Mexican government to implement border-crossing changes, the Trump administration has made several abrupt policy changes. Most recently, on December 20, 2018, the secretary of Homeland Security announced that the United States was unilaterally implementing Migration Protection Protocols (M.P.P.) that require asylum applicants to wait in Mexico while their claims are processed. The secretary of Homeland Security reportedly stated this policy would not apply to unaccompanied minors, but the official statement does not mention this exception, and there is confusion regarding the details and legality of the plan.

Nations that refuse to accept returnees are put on a list of recalcitrant countries, and the United States retaliates by refusing to permit citizens of those nations to visit here.

The unilateral M.P.P. change may be an attempt to force Mexico to sign a Safe Third Country agreement similar to the one that currently exists between the United States and Canada. The Canada-U.S. Safe Third Country Agreement designates each country as safe for refugees and requires individuals seeking protection to request it in the first safe country to which they travel: “Both governments trust that the other can make fair determinations on each refugee claim received. As such, refugees who claim asylum in the United States cannot do so in Canada (and vice versa).” 

Anyone who travels from one country to the other and applies for asylum will be returned to the first country (and must be accepted for return) within 90 days unless an exception, such as unaccompanied minor status, applies. But Canadian immigrant advocacy groups question whether the United States is a safe country for refugees and are gathering evidence to file a legal challenge to the agreement.

The U.S. government uses various diplomatic strategies to encourage nations to accept returning migrants, including the carrot-and-stick approach of granting or withholding foreign aid. It has been reported, for example, that President Trump has offered to pay Mexico to deport migrants from Mexico to Central America. The United States currently pays all costs of deporting aliens from the United States. Migrants who accept voluntary departure typically pay the cost of their own removal, but hospitals may pay for medical repatriation to avoid long-term care for uninsured migrants. Nations that refuse to accept returnees are put on a list of recalcitrant countries, and the United States retaliates by refusing to permit citizens of those nations to visit here.

Even when other nations are willing to accept returnees, U.S. law prohibits the return of individuals who face torture in their homelands.

Even when other nations are willing to accept returnees, U.S. law prohibits the return of individuals who face torture in their homelands. President Trump recognized this limitation when he excluded those eligible for withholding of removal pursuant to the Convention Against Torture from his presidential proclamation denying asylum rights to migrants who illegally cross the Mexican border. The Supreme Court’s refusal to lift a lower court injunction prohibiting implementation of Mr. Trump’s asylum ban is another lesson in the limitations of executive authority to control the deportation of aliens.

An estimated 10 million to 12 million deportable persons (illegal entrants, visa violators, and convicted criminals) live in the United States. In fiscal year 2018, Immigration and Customs Enforcement removed 256,085 of them. As Mr. Trump enters his third year in office, he may be realizing that the rule of law puts limitations on governments as well as immigrants. The United States is not unique in desiring control over who lives within its borders. Irregular migration is a global problem that requires global cooperation.

This story has been updated since publication to reflect the (temporary) resolution of the partial government shutdown.

Ellen K. Boegel is America’s contributing editor for legal affairs.