Next month it will be 10 years since District of Columbia v. Heller, the landmark case in which the Supreme Court acknowledged that the Second Amendment protects an individual right to armed self-defense. In that time the Court has done almost nothing to clarify the contours of that right.

The two exceptions are McDonald v. Chicago, the 2010 case in which the Court said the Second Amendment constrains states and cities as well as the federal government, and Caetano v. Massachusetts, a 2016 case involving a ban on stun guns in which the Court reiterated that weapons covered by the Second Amendment are not limited to those that are suitable for warfare or those that were in common use when the amendment was enacted. Critics, including Justices Clarence Thomas and Neil Gorsuch, frequently complain that the Court is neglecting the Second Amendment, letting judges who are hostile to gun rights flout Heller by upholding unconstitutional restrictions on firearms.

Duke law professor Joseph Blocher and Eric Ruben, a fellow at the Brennan Center for Justice, challenge that account, arguing that lower courts for the most part are simply applying the Second Amendment exceptions drawn by Heller. While there is some truth to that claim, it underestimates both the extent to which judges have ignored the implications of Heller and the extent to which that decision left important issues unresolved.

Blocher and Ruben analyzed every Second Amendment case decided by state and federal courts between June 26, 2008, when Heller was published, and February 1, 2016. Their broadest conclusion, consistent with what earlier studies have found, is that Second Amendment claims generally fail. They were successful in just 108 of the 1,153 cases in which they were raised, or 9 percent of the time. One reason for the high failure rate, Blocher and Ruben say, is that three-quarters of the claims were raised in criminal cases, where they were typically tacked on by "defendants facing serious charges," who "have every incentive to make whatever arguments they can get away with."

More generally, Blocher and Ruben argue, Second Amendment claims usually fail because they are usually weak. "The language of Heller makes it clear that some kinds of claims are flawed from the outset," they write. "Most fail precisely because of limitations that Heller itself places on the right to bear arms."

Justice Antonin Scalia, who wrote the majority opinion in Heller, seemed keen to assure readers that the decision would not sweep away widely accepted gun control laws that had been on the books for decades (citations omitted):

Like most rights, the right secured by the Second Amendment is not unlimited. From Blackstone through the 19th-century cases, commentators and courts routinely explained that the right was not a right to keep and carry any weapon whatsoever in any manner whatsoever and for whatever purpose. For example, the majority of the 19th-century courts to consider the question held that prohibitions on carrying concealed weapons were lawful under the Second Amendment or state analogues. Although we do not undertake an exhaustive historical analysis today of the full scope of the Second Amendment, nothing in our opinion should be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of arms.

That passage, Blocher and Ruben found, was quoted, "at least in part," by 60 percent of the judicial decisions they examined. But it's quite a leap to conclude that all those decisions must have been consistent with Heller, let alone consistent with the Second Amendment.

"This language from Heller gives constitutional blessing to a potentially wide range of regulation," Blocher and Ruben write in Vox. "So it should be unsurprising that the vast majority of the cases citing it go on to reject the Second Amendment claim and uphold the challenged law. Even when courts do not explicitly cite this particular passage in upholding gun laws, they often rely on other precedents that do so. That explains why the percentage of cases citing it has been steadily declining, as courts start to cite their own prior decisions that incorporate Heller's list of exceptions."

Notably, Heller's list of exceptions does not include bans on so-called assault weapons. To the contrary, Heller says the Second Amendment encompasses weapons "in common use" for "lawful purposes," a description that plainly applies to the guns targeted by such laws, since Americans own more than 16 million of them and almost never use them to commit crimes. State and federal judges nevertheless have upheld "assault weapon" bans since Heller, arbitrarily deeming these guns to be outside the scope of the Second Amendment.

Scalia did note that "prohibitions on carrying concealed weapons" were upheld by most of the 19th-century courts that considered them. But since those laws allowed people to carry guns openly, Scalia's observation hardly qualifies as an endorsement of the highly implausible proposition that the right to keep and bear arms does not extend beyond the door of a gun owner's home. As Thomas observed when the Supreme Court declined to hear an appeal of a 9th Circuit decision upholding California's restrictive carry permit law, it is "extremely improbable that the Framers understood the Second Amendment to protect little more than carrying a gun from the bedroom to the kitchen."

Although there are circuit splits on both of these issues, the Court has refused to resolve them. Nor has it clarified what level of scrutiny is appropriate in Second Amendment cases, another area where the courts are all over the map. As Blocher and Ruben note, "the justices have declined dozens of opportunities to expound on the right to keep and bear arms," a pattern that led Thomas to accuse his colleagues of treating the Second Amendment as a "constitutional orphan."

Where gun rights advocates see uncertainty, inconsistency, and disrespect for a constitutional guarantee, Blocher and Ruben see evidence that "courts are normalizing the post-Heller Second Amendment and treating it like other constitutional rights." By that they mean that the right to keep and bear arms is "subject to exceptions, some of which are derived from history, and to regulations that further certain important government interests."

These exceptions, which Blocher and Ruben say epitomize "'normal' constitutional law," are threatening to swallow the rule. The other part of normal constitutional law, the part that protects fundamental rights and overturns restrictions inconsistent with them, could use a boost from a Supreme Court that has been silent on this subject for too long.