Lost in the avalanche of commentary on Associate Justice Anthony M. Kennedy’s retirement from the Supreme Court are its potential ramifications for the U.S. role in the world. Over the past three decades, Kennedy has shepherded an evolving, increasingly productive relationship between the United States and international law. Whoever succeeds him will likely take a more conservative approach, setting up a potential confrontation between a sovereignty-obsessed America and the international rule of law.

The proper place of international law in U.S. law and jurisprudence—the subject of the legal field known as “foreign relations law”—is a political minefield. It generates vigorous, sometimes vituperative debate among constitutional scholars, including sitting Supreme Court justices.

At first glance, this controversy seems surprising. After all, the U.S. Constitution (Article 6, Section 2) designates treaties to which the United States is party as the “supreme Law of the Land,” alongside the Constitution itself and U.S. statutes enacted under it. The United States also recognizes the authority of customary international law, or that body of law that has emerged from enduring practices of states.

The Founding Fathers, moreover, were well read in and supportive of international law. In 1793, John Jay, the first Chief Justice of the United States, opined that the “peace, prosperity, and reputation of the United States, will always depend on their fidelity to their engagements”—that is, their respect for international legal obligations. A decade later, Jay’s successor, John Marshall, established what became known as the Charming Betsy Doctrine, arguing, “An act of Congress ought never to be construed to violate the law of nations if any other possible construction remains.”

If only it were that simple. In practice, American lawyers, policymakers, and politicians continue to debate the status of international law and its relationship with U.S. domestic law. These disagreements were front and center a century ago, when the U.S. Senate considered and ultimately rejected membership in the League of Nations. They erupted again in the 1950s in the near passage of the Bricker Amendment, which would have placed extraordinary political and procedural hurdles in the way of U.S. ratification of multilateral treaties.

Such debates have only intensified since the end of the Cold War. An entire cohort of conservative legal scholars, christened “new sovereigntists,” has emerged. They are adamant that trends in international law undermine U.S. independence by threatening the sanctity and integrity of its constitutional system of government.

These complaints focus on several alleged indignities. Among other things, self-styled sovereigntists decry what they perceive as the proliferation of intrusive multilateral treaties that infringe on domestic policy and regulations; the cross-border activism of left-wing U.S. advocacy groups seeking to bind the United States to a globalist agenda and UN conventions; the tendency of progressive legal scholars to create instant customary international law by elevating still-contested international norms; and the growing tendency of U.S. courts—including the Supreme Court—to make reference to the reasoning and rulings of foreign counterparts in their own legal decisions.

On this last issue Justice Kennedy emerged as a bête noire for constitutional “originalists.” He earned their animus by repeatedly citing foreign jurisprudence in pivotal court decisions in which he sided with his more liberal counterparts. Kennedy’s opinions in those cases rejected the conservative notion that the U.S. Constitution should be hermetically sealed, to avoid contagion from legal reasoning and trends in other lands, even fellow democracies.

Among Kennedy’s loudest critics was John Bolton, a sovereignty warrior who now serves as President Trump’s national security advisor. From his former perch at the American Enterprise Institute, Bolton consistently argued that foreign legal influences can only adulterate and contaminate U.S. constitutional reasoning.

For years, Kennedy’s main antagonist was fellow Associate Justice Antonin Scalia. In a series of memorable court cases, the two tangled over the propriety of referencing the findings of foreign courts in their decisions. One instance occurred in 2005, when Kennedy, the Court’s swing voter, penned the majority opinion in Roper v. Simmons. That 5-4 decision struck down the juvenile death penalty as a violation of the Eighth Amendment’s protections against cruel and unusual punishment. In his opinion, Kennedy cited “evolving standards of decency,” noting the “overwhelming weight of international opinion” against putting minors to death. “The United States now stands alone in a world that has turned its face against the juvenile death penalty,” he observed.

Scalia’s dissent—joined by Chief Justice William Rehnquist and Associate Justice Clarence Thomas—was withering. “What a mockery today’s opinion makes.... The court thus proclaims itself sole arbiter of our Nation’s moral standards—and in the course of discharging this awesome responsibility purports to take guidance from foreign courts and legislatures.” In the minority’s view, “the basic premise of the Court’s argument—that American law should conform to the laws of the rest of the world—ought to be rejected out of hand.”

Scalia and Kennedy traded similar barbs on other occasions. At the root of their long-running skirmish were two fundamental questions: First, should interpretations of the U.S. Constitution be insulated from or open to influence from foreign legal decisions and trends? Second, if the Constitution is opened to foreign influence, what, if any limits should be placed upon that impact?

For legal conservatives, the fundamental objection to referencing foreign legal materials is that it injects impurities into what should remain a self-contained constitutional tradition dating back to 1787. Beyond “inviting manipulation,” in Scalia’s view, the selective invocation of foreign legal sources risks transforming the U.S. judiciary into a quasi-legislative branch, allowing it to intrude on congressional competence by creating new law.

The Court’s more progressive wing, embodied by Associate Justice Stephen Breyer, is more tolerant of legal cross-pollination. It recognizes that the United States cannot afford to be insulated from the world behind an impermeable cellophane wrapper. Moreover, U.S. judges are already involved in an ongoing transnational legal conversation about, among other things, fundamental standards of human dignity. Finally, progressive jurists find merit in considering how judges and courts in other countries, particularly democracies, have come to their conclusions when grappling with similar cases and dilemmas.

In repeatedly siding with Breyer and other members of the Court’s liberal wing, Anthony Kennedy alienated Constitutional originalists. Those conservatives are now ascendant in the Trump administration, and they are determined that Kennedy’s successor not repeat the latter’s apostasy.

Jay Sekulow, a member of Trump’s legal team who is helping the president screen potential picks to replace Kennedy, made that clear Wednesday evening. Speaking on Sean Hannity’s Fox News show, he declared that any successful candidate for the Supreme Court must reject any reference to foreign courts. The Republican Party endorsed the same line at its 2016 convention in Cleveland. “The legitimate powers of government are rooted in the consent of the American people,” the GOP platform declared. “Judicial activism that includes reliance on foreign law or unratified treaties undermines American sovereignty.”

This conservative determination to insulate U.S. foreign relations law from foreign legal trends is both unrealistic and self-defeating. Whether or not they explicitly acknowledge it, U.S. judges and justices are already exposed to foreign legal cases, and they often interact with their foreign counterparts. It is better to acknowledge these influences honestly than to pretend they do not exist.

The more relevant question is the relative weight that judges, including Supreme Court Justices, should give to any foreign legal materials in crafting their opinions and ruling on cases before them. Here, there is room for compromise. Overwhelmingly, U.S. legal scholars of all stripes reject permitting foreign cases to determine the outcome of U.S. cases. The wisest balance is one that retired Associate Justice Sandra Day O’Connor proposed in a celebrated 2002 address to the American Society of International Law: “Although international law and the law of other nations are rarely binding upon our decisions in U.S. courts,” she reasoned, the “conclusions reached by other countries and by the international community should at times constitute persuasive authority in American courts.”

Such an open-minded approach could also help restore U.S. leadership in shaping international law. For much of the past century, the global flow of legal influence was one way—from the United States to the rest of the world. No longer. The Supreme Court, once a historic guide to other nations, is gradually losing its pole position as a primary source of international influence on the high courts of other nations, and its reluctance to engage its foreign counterparts simply accelerates this trend. For as Associate Justice Ruth Bader Ginsburg asked in 2008, “If we don’t cite them, why should they look to us?”

As Breyer points out in The Court and the World, the Supreme Court can make modest references to legal proceedings in like-minded nations without sacrificing its sovereignty. Contrary to the Trump administration’s assumptions, American internationalism and American independence are fully compatible. That’s worth bearing in mind as we head into the July Fourth holidays—and as we consider who might be a worthy successor to Anthony Kennedy.