Editor's note: Sarah Brady is chairwoman of the Brady Campaign to Prevent Gun Violence, an organization that aims to reduce the number of gun deaths and injuries.
(CNN) -- When the "Brady Handgun Violence Prevention Act" went into effect 20 years ago this month, America took a historic stand against gun violence. It was the first federal law to require that licensed dealers refer every gun sale to law enforcement for a background check.
The law honored my husband, Jim Brady, who had been shot in the head in 1981 by John Hinckley Jr, a mentally ill man who attempted to assassinate President Reagan. The shooting left Jim permanently impaired physically and cognitively.
Since February 28, 1994, according to the Bureau of Justice Statistics, background checks have stopped more than 2 million gun purchases by "prohibited purchasers" like convicted felons, domestic abusers, the dangerously mentally ill and fugitives—people who we all agree should not have guns. It's easy to imagine how many lives were saved and how many disabling injuries prevented thanks to Brady background checks.
But a lot has changed over the past two decades, and people who wouldn't pass a background check have found other ways to procure guns easily through unlicensed sales at gun shows or on the Internet, where background checks are not required.
The corporate gun lobby would like us to think these unlicensed sales are transactions between family members and hunting buddies, but the truth is that thousands of guns are sold legally each day without a background check, thereby potentially putting guns directly in the hands of criminals.
In fact, websites like Armslist.com boast upward of 70,000 listings from private sellers, many touting "No background check" as a selling feature. As a result, an estimated 40% of gun sales today occur without a Brady background check. Many of these sales have deadly consequences.
Take Zina Daniel, a victim of domestic violence who procured a restraining order against her estranged husband, making him unable to pass a background check. He bought a semiautomatic handgun from a private seller online, where he didn't need a background check. He used that gun to kill Zina and two others and wound four more at a nail salon.
Let's think about background checks in another way. Imagine if Zina's husband were on the no fly list and was one of 40% of airline passengers the Transportation Security Administration allowed to fly without undergoing a security screening. Would Americans feel safe in the air in this scenario? Not likely. Yet that is precisely the percentage of gun purchases made daily without a background check.
So what's the solution? Congress needs to finish the job the Brady law so effectively started to ensure that guns are kept out of the hands of people who should not have them.
Congress must pick up where it left off last April when, to Jim's and my great disappointment, Senate legislation to expand Brady background checks fell short. The bill received a majority 54 votes, including the support of six "A-rated" National Rifle Association senators, two of whom were the lead sponsors. The American people support this legislation.
In fact, 90% of Americans support universal background checks covering all online sales and gun shows. Three out of four NRA members and 80% of gun owners agree that the scope of background checks needs to be expanded.
In 2013, after the horrific tragedy of the school shooting in Newtown, Connecticut, eight states passed meaningful gun regulations. These laws could save lives and prevent injuries. Let's keep moving forward. Let's finish the job, expand Brady background checks and help keep guns out of the hands of the wrong people.
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The opinions expressed in this commentary are solely those of Sarah Brady.