The Biden administration announced a "historic" new rule on Thursday that aims to reduce gun violence by closing the so-called "gun show loophole" and requiring background checks for firearms sold online and at gun shows. The rule, published in the federal register by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), clarifies who is considered to be "engaged in the business" as a firearms dealer and expands the definition to include more sellers.

"Under this regulation, it will not matter if guns are sold on the internet, at a gun show, or at a brick-and-mortar store: if you sell guns predominantly to earn a profit, you must be licensed, and you must conduct background checks," Attorney General Merrick Garland said during a press call announcing the measure. "This regulation is a historic step in the justice department's fight against gun violence. It will save lives."

The rule, which follows a three-month consultation period that attracted nearly 388,000 comments, is set to take effect in 30 days. It is the latest in a series of unilateral steps taken by the Biden administration to tighten gun laws, highlighting the difficulty of getting legislation through Congress.

According to the White House, an estimated 22% of guns owned by Americans were acquired without a background check, and the new rule is expected to require about 23,000 more individuals to obtain a federal firearms dealer license. "It's not safe for innocent, law-abiding Americans. In fact, it's doggone dangerous," said ATF Director Steven Dettelbach, referring to the "large and growing black market of guns being sold by people in the business of dealing and doing it without a license."

The rule is an extension of the 2022 bipartisan Safer Communities Act, which stated that all persons "who devote time, attention, and labor to dealing in firearms as a regular course of trade or business to predominately earn a profit" would be considered a dealer. Inter-family transfers of firearms and occasional sales to enhance a collection will not be presumed business transactions, according to a White House spokesperson.

Vice President Kamala Harris, who leads the first federal gun violence prevention office, emphasized the importance of the new rule in preventing gun violence. "For decades, many dealers who sell weapons someplace other than the traditional gun store, say a gun show or flea market, or through social media, have gotten away without conducting background checks," she said. "Every year, thousands of unlicensed dealers sell tens of thousands of guns without a single background check to buyers who, if they had been required to pass a background check, would have failed, for example, domestic abusers, violent felons and even children."

President Joe Biden, who has repeatedly urged Congress to pass tougher gun regulations, including a ban on private ownership of assault weapons, said in a statement that he has spent time with people who lost loved ones to gun violence and is taking action to ensure fewer guns are sold without background checks. "This is going to keep guns out of the hands of domestic abusers and felons. And my Administration is going to continue to do everything we possibly can to save lives," he said.

The Department of Justice estimates that there are over 20,000 unlicensed sellers who are selling firearms through online advertisements, gun shows, and other means, in addition to the more than 80,000 licensed gun dealers in America. Administration officials are confident that the new rule is legal and will withstand potential challenges in court.

"Strong regulations like this one are not in conflict with the Second Amendment," a senior administration official told ABC News. The rule is expected to close both the "gun show loophole" and the "fire sale loophole," which allows firearms dealers who go out of business or lose their license to liquidate their inventory without conducting background checks.