As J.D. Tuccille noted this morning, "universal background checks" are emerging as a leading contender for the something that must be done by Congress in response to last month's massacre at Sandy Hook Elemenetary School. "There's a natural gravity that happens toward the ['assault weapon'] ban in the wake of tragedies," Dan Gross, president of the Brady Campaign to Prevent Gun Violence, tells The New York Times. “But it's very important to point out that background checks could have an even bigger impact."

Although the impulse to demand a ban on "assault weapons" after a mass shooting does resemble a reflex, in the sense that it is automatic and entails no thought, I would not call it "natural." It is a conditioned response instilled by people like Gross, who continue to peddle the lie that there is something uniquely dangerous about the guns included in this arbitrarily defined category. But I will agree with Gross on this point: Since reinstating the federal ban on "assault weapons" will have zero effect on the frequency of mass shootings or the number of people killed in them, expanding the background check requirement could be almost totally ineffective and still have a bigger impact.

That does not mean it is a good idea, however. Here are some questions to keep in mind if, as the Times predicts, "universal background checks" get a warmer reception from Congress than Dianne Feinstein's latest hodgepodge of "military characteristics":

1. How universal? After the 1999 massacre at Columbine High School, Colorado voters approved a ballot measure that requires everyone who buys firearms at a gun show to undergo a federal background check. If the seller is not a licensed gun dealer, he has to get someone who is to run the check. According to the Coalition to Stop Gun Violence, five other states (California, Illinois, New York, Oregon, and Rhode Island) have similar rules, while an additional three states (Connecticut, Maryland, and Pennsylvania) require background checks at gun shows only for handguns. (There are also seven states—Hawaii, Iowa, Massachusetts, Michigan, New Jersey, North Carolina, and Nebraska—that require handgun buyers to obtain permits, a process that involves a background check.) Now Colorado Gov. John Hickenlooper wants to go further, requiring background checks for private sales that do nor occur at gun shows, which are said to account for 40 percent of gun purchases in his state. That policy seems tantamount to banning private sales, since a licensed dealer with access to the National Instant Check System would have to be involved in every transaction. And if Hickenlooper is serious about making the requirement universal, simply giving your guns to someone—a father passing his hunting rifle to his son, for instance—also would have to be criminalized.

2. How would the requirement be enforced? The Washington Post reports that the gun control task force headed by Vice President Joe Biden, which is expected to make its recommendations next week, "is seriously considering measures backed by key law enforcement leaders that would require universal background checks for firearm buyers [and] track the movement and sale of weapons through a national database." To make the background check requirement stick, you have to know where the guns are at any given time and when they change hands. So now we are talking about a national registry of gun owners, enabling the federal government to make sure everyone who obtains a firearm is allowed to have one. If he's not, presumably he can expect a not-so-friendly visit from federal agents, who might merely confiscate the gun but could also arrest him for violating the Gun Control Act of 1968, which is punishable by up to five years in prison. The Times reports that "some [Obama administration] officials would like to expand mandatory minimum sentences for gun law violations."

3. Do we want better enforcement? As I noted last month, the categories of people prohibited by federal law from buying or owning guns are absurdly broad, including the 40 million or so Americans (probably considerably more) who qualify as "unlawful user[s] of...any controlled substance" and anyone who has been convicted of a felony, whether or not it involved violence or even a victim. Universal background checks, combined with the improved data collection that also is widely perceived as an eminently sensible response to mass shootings, would unjustly strip millions of people of their Second Amendment rights and subject them to criminal penalties for actions that harm no one.

4. How is this supposed to prevent mass murder? Northeastern University criminologist James Alan Fox, an expert on mass shootings, notes that "most mass murderers do not have criminal records or a history of psychiatric hospitalization," so "they would not be disqualified from purchasing their weapons legally." And if they were, he adds, "mass killers could always find an alternative way of securing the needed weaponry, even if they had to steal from family members or friends."