Supporters of the legislation say it builds on existing infrastructure and harnesses law enforcement expertise to try to prevent gun violence without pre-emptively removing guns or further regulating sales — both nonstarters for Second Amendment advocates.

But skeptics say that even if credit card companies, banks and retailers agree to work together to disclose detailed information about sales, the federal government would need a system for analyzing huge amounts of data and deciding when and how to respond.

An effective program would have to track credit card purchases of guns and ammunition as well as equipment such as body armor and night-vision goggles across multiple retailers.

“Banks, credit card companies and retailers have unique insight into the behavior and purchasing patterns that can help identify and prevent mass shootings,” said Wexton, whose plan has the backing of Everytown for Gun Safety, a national gun-control organization. “The red flags are there — someone just needs to be paying attention.”

Wexton, a freshman lawmaker and former prosecutor from Loudoun County, made gun violence a centerpiece of her 2018 campaign. Four Republicans are running for the nomination to challenge her next year.

Gun policy was a top issue for Virginia voters a month before the Nov. 5 state election that gave Democrats control of the House of Delegates and Senate for the first time in a generation, according to a Washington Post-Schar School poll.

Democrats have made gun control a priority since former Gov. Terry McAuliffe’s 2013 campaign, but the issue took on urgency after the May 31 shooting at a Virginia Beach municipal building where a gunman killed 12.

In the poll, 3 of 4 voters rated gun policy as a “very important” issue, and majorities supported background checks and “red flag” laws allowing authorities to take weapons away from people deemed dangerous. A majority also backed statewide bans on assault weapons and high-capacity ammunition clips, as well as limiting gun purchases to one per month.

The Democratic-controlled U.S. House passed legislation to expand background checks, but the bill is stalled in the GOP-controlled Senate.

Wexton’s latest bill, the Gun Violence Prevention Through Financial Intelligence Act, would give the Financial Crimes Enforcement Network, a bureau of the Treasury Department, a year to identify barriers to collecting purchase data.

The bill directs the network to consult with the FBI; the Bureau of Alcohol, Tobacco, Firearms and Explosives; and firearms sellers. One challenge could be obtaining details about items purchased, and the effectiveness of the program would hinge on the willingness of retailers to share information about specific firearms and accessories.

Many of those responsible for the deadliest shootings of the past decade financed their attacks using credit cards, a 2018 New York Times investigation found.

In a May interview with Bloomberg, the chief executive of Mastercard said his company does not have the information to track potentially suspicious purchases.

Joseph Moreno, a former federal prosecutor and FBI consultant who is a partner at the financial services law firm Cadwalader, said moderates may be open to Wexton’s legislation.

“It seems like moderate middle ground that privacy and Second Amendment advocates should be able to meet in the middle on,” he said. “We’re not talking about banning any kind of purchases or a federal registry.”

However, he noted that tracking could also discourage bad actors from using credit cards altogether. Cash purchases would make the transactions impossible to follow.

“It’s the kind of thing that needs to be explored if we’re going to be serious about addressing lone wolf terrorism,” he said. “But the devil’s in the details.”