The court said that legislators can continue to identify sensitive areas. But because the Bruen majority didn’t explain what counts as “sensitive,” we can expect that places as varied as college campuses, sports stadiums, bars, airports, domestic violence support centers and the sidewalks in front of lawmakers’ homes will become the next battlegrounds in litigation over the right to keep and bear arms.

In Bruen, Justice Clarence Thomas, writing for the majority, made the judgment that was expected: The Second Amendment protects “an individual’s right to carry a handgun for self-defense outside the home.” But as Justice Brett M. Kavanaugh and Chief Justice John G. Roberts Jr. noted in a concurring opinion, “properly interpreted, the Second Amendment allows a ‘variety’ of gun regulations,” including “laws forbidding the carrying of firearms in sensitive places such as schools and government buildings,” restrictions the court had endorsed in two prior decisions.

Conservatives sound like anti-racists — when the cause is gun rights

But how are lower courts to determine whether a place is sufficiently “sensitive” to prohibit firearms? According to Thomas, history and analogical reasoning will supply an answer. Because gun prohibitions near “legislative assemblies, polling places and courthouses” were uncontroversial in the past, he wrote, “courts can use analogies to these historical regulations” to determine what 21st-century areas are “sensitive” enough to ban guns.

This is awfully slender guidance from which to build a Second Amendment doctrine. The cabin of a commercial airliner feels pretty “sensitive” to most Americans, although it doesn’t bear any obvious resemblance to “legislative assemblies, polling places and courthouses.” Of course, that doesn’t mean there are no historical resources from which to draw analogies. The well of English and American law that forms the source of this “preexisting” Second Amendment right is deep. Harvard University prohibited guns on campus as far back as 1655, as did public institutions like the University of Virginia in 1825 and the University of North Carolina in 1829. In the 1800s, Missouri, Texas and the Oklahoma territory kept firearms and other weapons from places where people assembled for educational, literary, scientific or social purposes. These American laws have roots in Anglo prohibitions on weapons at “fairs” and “markets” that stretch back to the reign of King Edward III.

Before Bruen, lower courts had held that national parks and the parking lots of rural post offices were sensitive, and had indicated that libraries, museums, hospitals and day-care centers may also ban guns.

As Timothy Zick and Diana Palmer wrote recently in the Atlantic: Both red and blue states have created an archipelago of “sensitive places,” such as “public transit, polling places … athletic facilities, public swimming pools, riverboat casinos, school-bus stops, pharmacies, business parking lots, public highways, amusement parks, zoos, liquor stores, airports, parades, demonstrations, financial institutions, theaters, hotel lobbies, tribal lands, and even gun shows.” All these sensitive-place designations are now subject to challenge as insufficiently analogous to regulations that existed in the past.

Lower courts have held, unhelpfully, that what makes a place sensitive are “the people found there” or the “activities that take place there.” The implication is that guns may be prohibited from areas for reasons separate from personal safety, a point I’ve argued elsewhere. Long-standing historical prohibitions on guns on election day, or at polling places, or in schools, ballrooms, fairs, markets and public assemblies, for example, suggest that our ancestors’ concern was not only, or even primarily, with physical safety, but also with fostering a robust civic life that’s difficult to achieve in the presence of private arms.

On the other hand, some gun rights advocates insist that physical safety is the only legitimate reason to designate a place sensitive. And relatedly, such advocates say, a place can only forbid private weaponry if it supplies physical security through means such as guards or metal detection devices. If not, guns must be allowed.

Because Bruen gave little guidance as to why places are sensitive, lower courts are left with plenty of historical grist for making analogies, but no predictable way to decide whether the analog is relevantly similar. Justice Stephen G. Breyer aptly asks in his dissent, “What about subways, nightclubs, movie theaters, and sports stadiums?” How a 130-year-old regulation on guns at a public exhibition compares to a ban on guns at a 21st-century music concert is not at all apparent. Much less how a criminal prohibition on firing guns from the decks of riverboats resembles one forbidding loaded guns in the overhead compartments of jet aircraft. Where there’s a lack of clarity, there will be litigation.

I do not believe the court planned to consign every federal judge to act as the gun zoning authority for every city and town in every state. I do not believe the court wants to evaluate block by block, street by street, the sensitivity of every neighborhood in the country. But until the justices provide more clarity on why guns can be prohibited in sensitive places, and what makes those places sensitive, that may well be what we get.