"The most critical improvement" to the federal "assault weapon" ban, according to the Violence Policy Center, "is to ensure that the term 'assault weapon' includes all guns that are, in fact, assault weapons." Don't think about that assertion too much; it might cause your head to explode.

The gun banners at the VPC are unfazed by the fact that "assault weapon" is not an objective category: They know one when they see it. Legally, however, "assault weapon" means whatever Congress says it means.

The 1994 ban, which is scheduled to expire next year but would be renewed by legislation recently introduced in the House and Senate, identifies several specific brands and models as "semiautomatic assault weapons." It also bans any semiautomatic gun that accepts a detachable magazine and has at least two features from a list of five (four in the case of shotguns).

Although the justification for the ban was that "assault weapons" are especially dangerous, the criteria Congress chose—including bayonet mounts, folding stocks, pistol grips, and barrel shrouds—for practical purposes have nothing to do with lethality. The targeted guns are distinguished mainly by their sinister, military-style appearance.

The VPC complains that "the gun industry moved quickly to make slight, cosmetic design changes in their 'post-ban' guns to evade the law." That was possible because the focus of the law—the essence of what makes a gun an "assault weapon"—is slight and cosmetic.

The VPC says the solution is a broader definition: Instead of two features from a list, for example, one should suffice. But that approach makes the difference between legal and illegal guns even slighter, while evading the basic question of why these weapons were singled out to begin with.

As President Bush's support for renewing the law reflects, the "assault weapon" ban is widely seen as the very model of reasonable gun control. Yet it is based on arbitrary distinctions unrelated to public safety or crime control.

The anti-gun lobby decided to target firearms that look like military weapons for tactical reasons. As the VPC's Josh Sugarmann observed in 1988, "The weapons' menacing looks, coupled with the public's confusion over fully automatic machine guns versus semi-automatic assault weapons—anything that looks like a machine gun is assumed to be a machine gun—can only increase that chance of public support for restrictions on these weapons."

The VPC continues to capitalize on this confusion. "Civilian assault weapons," it says, "are semiautomatic versions of military weapons designed to rapidly lay down a wide field of fire—often called 'hosing down' an area." Contrary to the impression left by that ambiguous statement, so-called assault weapons fire once per trigger pull, like any other semiautomatic.

Functionality aside, are "assault weapons" especially popular with criminals? Police statistics from across the country indicate that they represent 2 percent to 3 percent of guns used in crimes.

To get around the fact that "assault weapons" are rarely used by criminals, the VPC is now claiming that from 1998 through 2001 "one in five law enforcement officers slain in the line of duty was killed with an assault weapon." This estimate is padded by the inclusion of weapons that Congress does not define as "assault weapons" but that the VPC does. In any case, it indicates that the vast majority of cop killers use guns that no one considers to be "assault weapons."

Notice, too, that banning guns does not prevent them from being used in crimes, which makes you wonder what good even an "improved" ban could be expected to accomplish. Even if cop killers were fond of "assault weapons" and if passing a law could magically eliminate them, it's absurd to imagine that violent criminals could not find adequate substitutes.

The "assault weapon" ban sets a dangerous precedent precisely because the justification for it is so weak. It suggests that you don't need a good reason to limit the right to keep and bear arms, and it invites further restrictions down the road. As far as the gun banners are concerned, that is the whole point.

In 1996 Washington Post columnist Charles Krauthammer, who favors banning gun possession by civilians, conceded that the arguments advanced by supporters of the "assault weapon" ban were "laughable." The "only real justification" for the law, he said, "is not to reduce crime but to desensitize the public to the regulation of weapons in preparation for their ultimate confiscation."