On May 21, 2020, U.S. Secretary of State Mike Pompeo announced that the United States would withdraw from the Treaty on Open Skies. The treaty, which has been ratified by several former Soviet Republics and most North Atlantic Treaty Organization (NATO) members, allows states parties to conduct observation flights over each other's territory to build trust and transparency with respect to arms control. The treaty gives state parties a right to withdraw upon six months of notice, which Pompeo stated would be formally given by the United States on May 22. Pompeo described the U.S. withdrawal as a response to Russian violations of the treaty and held open the possibility that the United States would rescind its notice of withdrawal in the event of full Russian compliance. U.S. allies in Europe reaffirmed their own commitment to the treaty and to working with Russia over disputes arising from it. The announced U.S. withdrawal raises significant issues of U.S. domestic law, as the Trump administration did not comply with preconditions to withdrawal that had been established by Congress in the National Defense Authorization Act for Fiscal Year 2020.

In a speech before the National Rifle Association (NRA) on April 26, 2019, President Trump announced that he was requesting the return of the Arms Trade Treaty (ATT) from the Senate and that the United States would unsign this treaty. Shortly thereafter, Trump issued a formal letter to the Senate requesting the ATT's return. As of late September, the Senate had not formally approved Trump's request. Nonetheless, on July 18, 2019, the Trump administration communicated to the secretary-general of the United Nations that the United States does not intend to become a party to the ATT and thus has no future legal obligations stemming from signature.

In July of 2019, the U.S. Senate gave advice and consent to protocols updating tax treaties with Spain, Switzerland, Japan, and Luxembourg, after a nearly decade-long period during which no tax treaties were approved by the Senate. This drought was primarily due to the privacy concerns of a single senator, Rand Paul of Kentucky, who deployed the Senate's procedural rules to increase the difficulty of the advice and consent process. Tax treaties with Hungary, Chile, and Poland, as well as a protocol to a multilateral tax convention, remained pending in the Senate Foreign Relations Committee as of mid-August of 2019.

With only three remaining members of what is supposed to be a seven-member body, the World Trade Organization's (WTO) Appellate Body may soon cease to function. Since 2016, the United States has blocked the reappointment of Appellate Body members and rejected over a dozen proposals to launch selection processes that could fill the remaining vacancies. As a lead reason for these blocks, the United States has cited concerns about the practice whereby members whose terms have expired continue to serve on appeals to which they were previously appointed. On December 10, 2019, the terms of two Appellate Body members will expire, leaving only one member remaining. Because the WTO's dispute settlement process requires three Appellate Body members for each appeal, WTO members will be unable to make any new appeals by this year's end unless a solution emerges to the current impasse.

The Arctic Council convened for the eleventh time in early May 2019 in Rovaniemi, Finland, for a two-day conference. On May 7, the Arctic Council released a Joint Ministerial Statement that affirmed the desire of the eight member states to work together to face upcoming challenges but made no substantive commitments and no mention of climate change. In remarks to the Council, Secretary of State Mike Pompeo expressed wariness about collective decision making and warned against potential effects of Chinese activity in the Arctic.

The Trump administration has continued its efforts to restrict immigration through a series of measures designed to limit the availability of asylum in the United States and to promote increased immigration enforcement in Mexico. In July of 2019, the Department of Homeland Security (DHS) and the Department of Justice (DOJ) promulgated an interim final rule disqualifying asylum applicants who transited through third countries without seeking protection in those countries. This rule immediately became the subject of ongoing litigation, and, in September of 2019, the Supreme Court stayed an injunction that had been issued against its enforcement, with two justices dissenting. At the international level, over the summer and early fall of 2019, threats of economic sanctions led Guatemala, El Salvador, Honduras, and Mexico to make agreements with the United States aimed at curbing unauthorized migration into the United States. Guatemala signed an agreement with the United States under which asylum applicants in the United States who had transited through Guatemala on the way could be returned to Guatemala to pursue their asylum claims. El Salvador and Honduras also reached agreements with the United States relating to migration. Mexico committed to increasing its efforts to stem the flow of unauthorized immigration through its borders and assented to the U.S. expansion of its Migrant Protection Protocols. The Trump administration has continued pursuing other tactics to limit immigration and the availability of asylum, including through the issuance of legal decisions by Attorney General William Barr and continued litigation surrounding the construction of a border wall.

On July 8, 2019, Secretary of State Mike Pompeo established a Commission on Unalienable Rights. The Commission will “provide the Secretary of State advice and recommendations concerning international human rights matters … [and] provide fresh thinking about human rights discourse where such discourse has departed from our nation's founding principles of natural law and natural rights.” The Commission has an initial two-year mandate. Democratic lawmakers have raised concerns that the Commission will circumvent existing structures and challenge LGBTQ+ protections and reproductive rights.

In the face of rising tensions between Iran and the United States, some members of Congress have urged the Trump administration to clarify whether it believes it has congressional authorization to use force against Iran. In June of 2019, the U.S. State Department issued a letter stating that it had not “to date” interpreted either the 2001 or the 2002 Authorization for Use of Military Force (2001 AUMF and 2002 AUMF, respectively) “as authorizing military force against Iran, except as may be necessary to defend U.S. or partner forces engaged in counterterrorism operations or operations to establish a stable, democratic Iraq.”

On June 10, 2019, the Supreme Court denied certiorari in a case in which the D.C. Circuit held that the United States could continue to detain an individual at Guantánamo Bay until the cessation of the hostilities that justified his initial detention, notwithstanding the extraordinary length of the hostilities to date. The case, Al-Alwi v. Trump, arises from petitioner Moath Hamza Ahmed Al-Alwi's petition for a writ of habeas corpus challenging the legality of his continued detention at the United States Naval Base at Guantánamo Bay. The Supreme Court's denial of certiorari was accompanied by a statement by Justice Breyer observing that “it is past time to confront the difficult question” of how long a detention grounded in the U.S. response to the September 11 attacks can be justified.