Today the U.S. Supreme Court struck down a federal criminal statute on the grounds that its language is so imprecise that it violates the Constitution. "When Congress passes a vague law," declared the majority opinion of Justice Neil Gorsuch, "the role of courts under our Constitution is not to fashion a new, clearer law to take its place, but to treat the law as a nullity and invite Congress to try again."

Writing in dissent, Justice Brett Kavanaugh championed a very different sort of role for the courts. "A decision to strike down a 33-year-old, often-prosecuted federal criminal law because it is all of a sudden unconstitutionally vague is an extraordinary event," Kavanaugh complained. "The Court usually reads statutes with a presumption of rationality and a presumption of constitutionality."

The case is United States v. Davis. At issue is a federal statute which, in the Court's words, "threatens long prison sentences for anyone who uses a firearm in connection with certain other federal crimes. But which other federal crimes?" That is where the debate over vagueness comes in. The law itself calls for enhanced sentencing in cases involving felonies "that by [their] nature, involv[e] a substantial risk that physical force against the person or property of another may be used in the course of committing the offense."

And what exactly does that mean? Opinions differ. And therein lies the problem. As Justice Gorsuch pointed out in his majority opinion, "even the government admits that this language, read in the way nearly everyone (including the government) has long understood it, provides no reliable way to determine which offenses qualify as crimes of violence." And "in our constitutional order," Gorsuch observed, "a vague law is no law at all" because it violates the core constitutional requirement that all federal statutes "give ordinary people fair warning about what the law demands of them."

Gorsuch's decision was joined in full by Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor, and Elena Kagan.

In his dissent, Justice Brett Kavanaugh, joined by Chief Justice John Roberts and Justices Clarence Thomas and Samuel Alito, attacked Gorsuch's ruling for taking the Court "off the constitutional cliff." Yes, the Supreme Court is supposed to "ensure that Congress acts within constitutional limits and abides by the separation of powers," Kavanaugh wrote. "But when we overstep our role in the name of enforcing limits on Congress, we do not uphold the separation of powers, we transgress the separation of powers."

In other words, Kavanaugh just called Gorsuch a judicial activist.

In previous criminal justice cases, Gorsuch has butted heads with Alito over the meaning and application of the Fourth Amendment. It looks like Gorsuch will now be butting heads with Kavanaugh in some criminal justice cases too.

The Supreme Court's opinion in United States v. Davis is available here.