Last December, U.S. President Joe Biden sought to end a controversial immigration program put in place by his predecessor, Donald Trump. That scheme, known as Title 42, relied on an old public health statute to expel more than 2.4 million migrants, including thousands of unaccompanied minors, at the southern border. But before Biden could end Title 42, a coalition of Republican-led states petitioned the U.S. Supreme Court to step in and block the federal government from winding down the expulsions. Without any hearing, and despite grave doubts about whether these states even had the legal right to lodge such a challenge, the Court summarily agreed: it forced Biden to continue the Trump-era program, which remains in place to this day.

The Court’s ruling reflected a growing judicial habit of embracing aggressive legal interpretations to issue decisions that could significantly limit what the United States can and cannot do in the world. Led by the U.S. Supreme Court, domestic courts are poised to reshape the implementation of a vast array of laws and regulations critical to U.S. foreign policy, affecting migration, the treatment of people detained on terrorism-related grounds, and the authority of government agencies crucial to diplomatic initiatives related to health, environmental, and technology policy. This legal activism comes at a time when Congress has largely withdrawn from foreign policy and when the country’s polarization has made it difficult for federal lawmakers to approve new international agreements, especially Senate-ratified treaties, or major statutory changes. As a result, the Biden administration’s foreign policy priorities depend ever more on whether executive branch initiatives invite the scrutiny of an emboldened and antagonistic judiciary.

These developments are at odds with the traditional view of the Supreme Court, which plays up its role as an adjudicator of specific disputes, not as a major driver of foreign affairs. Responsibility for that domain is thought to lie with the White House, the State Department, the Pentagon, and the Department of Homeland Security—entities to which the Supreme Court has historically deferred. But in a few short years, the Court under Chief Justice John Roberts has carved out a new, muscular role in foreign policy that goes well beyond immigration. In the last year alone, it has taken cases that affect transnational security cooperation, the regulation of financial risk, the legal responsibilities of social media companies that operate across borders, and U.S. leadership on climate change. It has done so in ways that buck precedent and stretch the power of the Court beyond its familiar bounds. In effect, the Supreme Court is not just the highest court in the land—it is well on its way to becoming a shadow ministry of foreign affairs.

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