On June 1, 2020, the Supreme Court unanimously held that the Convention on the Recognition and Enforcement of Foreign Arbitral Awards (New York Convention or Convention) does not conflict with domestic equitable estoppel doctrines that permit the enforcement of arbitration agreements by nonsignatories. The Court interpreted the text of the Convention as being silent on the issue of enforcement by nonsignatories and thus leaving this issue to domestic law. The Court noted that some postratification practice (including the recommendation of a UN commission) and the views of the executive branch were consistent with its conclusion, but it did not determine how much weight should be accorded to these sources.

In Opati v. Republic of Sudan, the Supreme Court upheld a $4.3 billion award of punitive damages against Sudan for its support of the 1998 bombings of U.S. embassies in Kenya and Tanzania. The Supreme Court held that Congress's 2008 amendments to the Foreign Sovereign Immunities Act (FSIA) authorized the plaintiffs to recover punitive damages from state sponsors of terrorism for acts committed prior to the enactment of these amendments. This case is part of a broader trend of U.S. litigation brought against states who are designated sponsors of terrorism or alternatively are deemed responsible for acts of terrorism within the United States.

President Trump decided in mid-April of 2020 to suspend U.S. funding for the World Health Organization (WHO) and to have his administration review its performance, contending that it was biased in favor of China and inept in its handling of the COVID-19 pandemic. In a letter to the WHO director-general a month later, Trump informed the director-general that his administration's review confirmed his accusations. He threatened that, unless the WHO implemented significant reforms, the United States would reconsider its membership in the organization. Less than two weeks later, on May 29, 2020, Trump announced his decision to terminate the U.S. relationship with the WHO. On July 6, the administration gave formal notice of U.S. withdrawal to the UN secretary-general, the depositary for the WHO Constitution. Assuming certain legal preconditions are satisfied and the notice of withdrawal is not revoked, the withdrawal will take effect on July 6, 2021.

On November 30, 2018, Canada, Mexico, and the United States signed an agreement renegotiating the North American Free Trade Agreement (NAFTA). By the spring of 2020, all three countries had approved this agreement—known in the United States as the United States-Mexico-Canada Agreement (USMCA)—through their respective domestic ratification processes. The USMCA entered into force on July 1, 2020, amid extended U.S.-Mexico and U.S.-Canada border restrictions due to the COVID-19 pandemic. On August 6, 2020, President Trump imposed tariffs on Canadian aluminum—tariffs that his administration had previously put in place in 2018 but had removed in 2019 in order to smooth the USMCA's path to ratification.

In the spring of 2020, the Appeals Chamber of the International Criminal Court (ICC) authorized the ICC's prosecutor to investigate alleged international crimes committed in Afghanistan. The Trump administration strongly condemned this decision. In an escalation of retaliatory measures against the ICC, President Trump signed an executive order authorizing economic sanctions against foreign persons involved in the investigation and visa restrictions against those persons and their immediate family members. The ICC described these actions as a threat to the rule of law.

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.