Americans overwhelmingly support background checks. Surveys show that 93 percent of Americans—including 83 percent of gun owners and 72 percent of NRA members—support criminal background checks for all gun sales.

But under pressure from the gun lobby, Congress and most states have failed to close the deadly loopholes in the background check system.

Federal law only requires licensed gun dealers to conduct background checks. That means that millions of guns are exchanged each year without a check—most often online or at gun shows through unlicensed “private sellers.” Felons, domestic abusers, the seriously mentally ill, and other dangerous people know about this loophole, and they exploit it every day.

It’s like having two lines at the airport—one with security, and one without. And criminals get to choose. That’s why criminals are flocking to unregulated online gun sales—where they can buy guns, with no background check and no questions asked.

Closing this unlicensed sale loophole is the simplest way to shut down criminals’ and other dangerous people’s easy access to guns. Background checks have blocked more than three million sales to dangerous people, and a background check takes only a few minutes to complete.

We also need to make sure the background check database is complete. States and federal agencies have failed to send hundreds of thousands of records to the national background check databases. Every missing record is another tragedy waiting to happen. The Virginia Tech shooter, who killed 32 people, was banned from buying guns because a court found him severely mentally ill. But he passed a background check because his records never made it into the system.

There is no better way to reduce gun deaths in America than strengthening the background check system.