Supreme Court nominee Brett M. Kavanaugh, left, with Sen. Michael Crapo (R-Idaho). (Bill O'Leary/The Washington Post)

Stephen I. Vladeck is a law professor at the University of Texas and co-editor of the online forum Just Security.

Unless the Supreme Court chooses to step in, the U.S. Court of Appeals for the District of Columbia Circuit has the last word in cases arising out of the detention or prosecution of noncitizens detained as “enemy combatants” at Guantanamo Bay. And no judge on that court has played a larger role in those cases than Brett M. Kavanaugh — President Trump’s nominee to replace Supreme Court Justice Anthony M. Kennedy.

Although reasonable minds may disagree on whether the differences are a feature or a bug, a review of Kavanaugh’s Guantanamo record clearly shows just how much distance there is between him and Kennedy — and, as a result, just how much his confirmation would shift the court’s center of gravity on these issues.

This shift matters not only because significant litigation continues to arise out of Guantanamo — where 40 men are still detained as military commissions grind forward — but also because of the implications Kavanaugh’s judicial philosophy could have on the Supreme Court more broadly. How might his excessively deferential view of the role that courts should play in national security cases move this vital area of the law over the course of a generation?

Start with Kennedy. In 2004, he joined Justice Sandra Day O’Connor’s governing opinion in Hamdi v. Rumsfeld, which upheld the military detention of a U.S. citizen captured on an Afghanistan battlefield, but only because international law had long accepted such detention of enemy forces as an incident of war. The O’Connor opinion made clear that, where international law and practice did not support a form of detention — such as “indefinite detention for the purpose of interrogation” — the relevant congressional statute “clearly” should not be construed to authorize such detention.

Similarly, in 2006, Kennedy — who routinely looked to international law in interpreting, among other texts, the Eighth Amendment — provided the pivotal fifth vote in Hamdan v. Rumsfeld, in which the court struck down the first round of military commissions created by President George W. Bush for several reasons, including because they did not comply with the Geneva Conventions. Two years later, Kennedy again cast the decisive vote — and wrote the majority opinion — in Boumediene v. Bush, in which the court held that Guantanamo detainees had a constitutional right to seek judicial review of their detention, and that an act of Congress purporting to foreclose such review was unconstitutional.

Kavanaugh, in contrast, has consistently questioned the relevance of international law in shaping the executive’s war powers and construing legislative authorizations. In one especially revealing and controversial 2010 case, he and Judge Janice Rogers Brown concluded that, notwithstanding the Hamdi decision, the courts should ignore international law — even the possibility that a detention might violate such law — in construing Congress’s authorization of the executive to hold the Guantanamo detainees. Indeed, Kavanaugh went so far as to argue that courts should decline to apply the age-old rule of interpretation that federal laws should, where fairly possible, be construed not to authorize breaches of international law. (The rest of the judges on the D.C. Circuit, apart from Kavanaugh and Brown, marginalized that analysis by concluding that it had been unnecessary to resolve the case at hand.)

In the context of the military commissions, Kavanaugh’s skepticism of international law has left him as the central defender of the government’s controversial claim that the commissions may constitutionally try offenses that are not international war crimes. In multiple opinions setting out this position, he has relied not on constitutional text — indeed, he conceded that “based solely on the text” of the Constitution, the defendant “might have a point” — but instead on historical precedents (such as the trial of the Lincoln assassination co-conspirators) that scholars have thoroughly debunked as supporting Kavanaugh’s claim.

More generally, Kavanaugh has been far more circumspect about the role of the courts than Kennedy. In one 2014 dissent, he suggested that Congress had validly barred the D.C. Circuit from reviewing any cases from the military commissions except through a post-conviction appeal. In a 2011 case involving a U.S. citizen detained in Iraq, he found no constitutional problem with a statute that prevented the courts from reviewing whether the detainee was about to be transferred to a country in which he reasonably feared torture. And in a 2009 case arising out of torture at Abu Ghraib, Kavanaugh joined Judge Laurence Silberman (over a rare and powerful dissent from Judge Merrick Garland) in barring state-law tort claims against a private military contractor, even though no federal statute required such a result.

To be clear, there is no question that Kavanaugh is a thoughtful, careful and exceptionally bright jurist. He is also unusually willing and eager to engage with arguments and scholarship that challenge his preconceptions. Notwithstanding those admirable qualities, however, Kavanaugh’s many opinions concerning Guantanamo and related matters make it crystal clear that his confirmation would make the court far more deferential to the president’s exercise of aggressive war powers, would diminish the long-standing role of international law as a means of shaping executive authority and understanding congressional authorizations, and would more generally weaken the role of the courts as a check on the political branches in this profoundly important area of law.