So how would this work? I asked the University of Chicago's Jens Ludwig, who has studied the issue in depth. His bottom line: A universal background check law could conceivably reduce gun violence. But it might also prove difficult to enforce.
Here's how the law is currently set up. "Let's say I live in Mississippi," explains Ludwig. "I drive to my local gun store, a federally licensed dealer. I have to do a background check to buy a gun. But once I pass that check, I can buy 50 Glocks and go to the parking lot and sell those guns out of the trunk of my car to anyone, no questions asked. The only constraint is that I can't knowingly sell a gun to someone disqualified from owning one. So long as the buyer isn't wearing a Riker's Island alumni hat, it's don't ask don't tell."
That's a significant exception. In the 1990s, Ludwig and Duke's Philip J. Cook published an analysis (pdf) finding that around 40 percent of all gun transactions occur in this secondary market. And criminals are particularly likely to take advantage of this market. By the late 1980s, surveys from the Bureau of Justice Statistics found that some 80 percent of those who used guns in crimes bought their weapons from the secondary market.
Things would be different under a universal background check system. Let's say I want to sell my gun. My colleague Dylan Matthews is interested. Instead of selling it directly to him, we might both have to travel to a federally licensed gun dealer, who would run the requisite background check on Dylan and facilitate the sale.
The big challenge, says Ludwig, would be enforcement. There are 300 million guns currently in circulation and the federal government doesn't have any data on who owns what. There's no national registry for guns. All the federal trace data shows is who originally bought the gun from a licensed dealer.
"So let's say a universal background check law passes and a gun I bought back in 2008 shows up on a Chicago crime scene a month from now," says Ludwig. "The police show up at my door and ask who I sold it to. I say I sold it before the [universal background check] passed and at that time I wasn't required to ask any questions." There would be no way for police to know if he had complied with the law or not.
Still, Ludwig isn't sure that this is a fatal flaw. "Most people who own guns are middle-class, law-abiding citizens," he says. "If you tell them to do a background check, I think they’ll do it voluntarily." And for those who prefer to evade the law, the government might have to provide more resources for police to do undercover gun buys on the secondary market—in order to ensure compliance. "That's never going to be perfect, but anything you can do to tighten the secondary market will help."
Would universal background checks reduce gun homicides? Ludwig thinks so. Recently, he and Cook found that the 1994 Brady Act, which required background checks at all federally licensed gun dealers, didn't reduce homicides at all. But, he says, that's likely because of the vast secondary gun market. "Anything that can help add friction to that secondary market has the potential to be very helpful."
The question, of course, is whether Congress will agree. The National Rifle Association has strongly objected to universal background checks — among other things, the group argues that only 10 percent of guns are purchased on the secondary market. (The NRA also disputes the idea that the current law amounts to a "gun-show loophole," pointing out that many of the people selling at gun shows are federally licensed dealers.)
On the flip side, universal background checks could prove popular with the public. In a recent Washington Post-ABC poll, 88 percent of Americans said they support a law requiring background checks in sales at gun shows, including 89 percent of Republicans.