Justice Neil Gorsuch got another opportunity to flex his libertarian muscle on Monday, authoring a 5–4 decision striking down a federal law that imposed harsher penalties on certain criminal defendants. Gorsuch joined the four liberals in United States v. Davis to declare the statute unconstitutionally vague, over the dissent of Justice Brett Kavanaugh and the remaining conservatives. The two Trump appointees sparred extensively in Davis, revealing a profound dispute over the role of courts and Congress in the criminal justice system.

Davis involves a federal statute that lengthens prison sentences for certain firearms offenders. It applies when a defendant uses a gun in a “crime of violence,” which is defined as an offense that “by its nature, involves a substantial risk that physical force against the person or property of another may be used in the course of committing the offense.” What does that mean? What is the “nature” of a crime? How much risk is “substantial”? It’s not exactly crystal clear, which creates a problem: The Supreme Court has held that overly vague criminal laws offend due process (by failing to give individuals notice of forbidden conduct) and separation of powers (by forcing the judiciary, not Congress, to define criminal conduct).

Indeed, this language almost perfectly mirrors the statute that SCOTUS struck down as unconstitutionally vague in last year’s Sessions v. Dimaya. So there was never much doubt how Davis would come out. Gorsuch began his opinion with a rococo paean to void-for-vagueness doctrine, declaring: “In our constitutional order, a vague law is no law at all.” He then explained why the law in Davis must be interpreted under what’s called the “categorical approach,” which requires courts to disregard a given defendant’s actual conduct and instead consider an “ordinary case” of the charged crime.

Here’s an example of how this works. Davis received a heightened sentence because he committed a “crime of violence”: conspiracy to commit robbery. Why is that considered a “crime of violence”? Imagine the typical robber and his typical conspiracy. Not the conspiracy in this case, but the ordinary conspiracy (whatever that might mean). Now ask: Is this typical robber you’ve conjured up using force while engaged in his typical conspiracy? If the answer is yes, then conspiracy to commit robbery is a “crime of violence” because “by its nature” it involves “physical force.” And voilà—you’ve just kept someone in prison for up to 25 more years.

Get Slate in Your Inbox Slate's daily newsletter, The Angle, rounds up the stories you need to read. We encountered an issue signing you up. Please try again. Please enable javascript to use form. Email address: Send me updates about Slate special offers. By signing up, you agree to our Privacy Policy and Terms Sign Up Thanks for signing up! You can manage your newsletter subscriptions at any time.

Confused? You should be. This approach is wildly unpredictable, as the court explained in Dimaya. But it’s compelled by the statute’s language, which does not ask juries to assess the facts of the crime at hand, but instead requires hypothesizing about some generic crime. When “we speak of the nature of an offense,” Gorsuch wrote, we’re talking about “what an offense normally … entails, not what happened to occur on one occasion.” Unfortunately for the government, this “obvious reading of the text” renders the law impermissibly vague, too blurry to give Americans notice of what conduct it might prohibit. “In our republic,” Gorsuch wrote, “a speculative possibility that a man’s conduct violated the law should never be enough to justify taking his liberty.”

To save the law, the government attempted to recast it as an inquiry into the defendant’s actual conduct. It invoked the canon of constitutional avoidance, which obligates the courts to avoid striking down a statute when it can identify an alternative constitutional interpretation. This claim prompted the most interesting and, arguably, important passage in Gorsuch’s opinion. Adopting a case-specific approach to avoid constitutional infirmities, he noted, would actually broaden the scope of the law because plenty of crimes that aren’t categorically violent might be executed in a violent manner.

The typical case of fraud, for instance, might be nonviolent. So under the categorical approach, those who perpetrate fraud while carrying a gun could avoid a sentence enhancement. But the details of a specific fraud offense may well involve “substantial risk [of] physical force.” And under the government’s case-specific approach, the statute in Davis could be extended to cover that offense. The government thus wanted SCOTUS to avoid the law’s constitutional flaws by expanding the number of crimes it encompasses.

Gorsuch has his own fairly radical reasons for questioning state power.

In response, Gorsuch laid down an important new rule: Constitutional avoidance may be used to narrow “construction of a criminal statute,” but it cannot be used to broaden one. If courts relied on the constitutional avoidance canon to construe a criminal statute to expand its scope, they “would risk offending the very same due process and separation-of-powers principles on which the vagueness doctrine itself rests.” They would also contravene the rule of lenity, which compels courts to interpret vague criminal laws in the defendant’s favor.

“[T]hat theory,” Kavanaugh huffed in dissent, “seems to come out of nowhere.” He insisted that Gorsuch’s “broadening/narrowing” principle was “novel” and unsound, with no basis in precedent. This allegation spurred a fascinating squabble between the two justices that revealed deeper philosophical disagreements. Kavanaugh may be right that no Supreme Court precedent has ever laid down Gorsuch’s rule—but that may be because it was never necessary to do so. Most vague criminal laws are salvaged by judicial tailoring: Courts merely shrink the number of offenses that qualify for punishment. The law in Davis, by contrast, is hydraulic, and Kavanaugh’s construction would only shift penalties toward a different, broader class of crimes. Few other statutes would trigger the same weird consequences.

It’s notable that Chief Justice John Roberts, who joined most of Kavanaugh’s dissent, declined to join this section. Only Justices Samuel Alito and Clarence Thomas, it seems, agree with Kavanaugh that courts can deploy constitutional avoidance to expand a criminal statute. That position reflects a conservative faith in government to apply the law fairly, a faith Gorsuch obviously lacks. It may be that Gorsuch wants to tear down much of modern American governance, but the liberal justices aren’t afraid of relying on his vote in the meantime to snatch progressive victories.

After all, it was Justice Ruth Bader Ginsburg, the senior-most justice in the majority, who assigned Davis to Gorsuch. She plainly trusted him to do the job right, and neither she nor her progressive colleagues had any apparent compunction about joining his staunchly libertarian opinion. Gorsuch has his own fairly radical reasons for questioning state power. But when his views align with those of the liberals, it allows the court to bolster constitutional protections that progressives hold dear.