Dan Helmer, a Democrat running for the nomination to challenge Rep. Barbara Comstock (R-Va.), released an undercover video showing Helmer purchasing a rifle at a gun show without a background check. (Dan Helmer for Congress)

A Democrat running for the nomination to challenge Rep. Barbara Comstock (R-Va.) strolled into a gun show in Chantilly last month and purchased a semiautomatic rifle in about 10 minutes without a background check, according to an undercover video produced by his campaign.

Dan Helmer, an Army veteran, said he bought a firearm similar to the one he carried in Iraq and Afghanistan to show how easy it is to legally obtain an “in­cred­ibly dangerous piece of weaponry that’s meant for war” from a private seller. He bought the gun less than two miles from a public school, he said.

While background checks are required for purchases at gun shows from federally licensed dealers, Helmer wants to close the “gun show loophole” that allows anyone to buy a weapon from an unlicensed seller without scrutiny.

The video is the latest volley in the six-way Democratic primary, in which each candidate is calling for tougher gun laws.

The issue took on new resonance after the school shooting in Parkland, Fla., and appeals to the female suburban voters who helped Gov. Ralph Northam (D) win last year — a victory Democrats in Virginia’s 10th District hope to replicate in November.

Dan Helmer, right, a Democratic candidate in Virginia’s 10th District House race, buys a semiautomatic rifle in a private sale at a gun show in Chantilly. (Dan Helmer for Congress)

The 2017 election represented a turning point for gun-control advocates. They cite exit polls that showed voters who care about gun policy were just as likely to turn out for Northam, who pledged stricter gun laws, as they did for Republican Ed Gillespie, who opposed new restrictions. Gun policy was the second-most-important issue for voters, ranking below health care and just above taxes.

Lori Haas, Virginia state director for the Coalition to Stop Gun Violence, said the “passion gap” has shifted as more Democrats cast ballots to make a statement about guns.

“Ralph Northam, who did not shy away from the issue on any level, won by almost 10 points,” she said. “I contend that gun violence prevention actually helped him increase his winning margin. I think we’ll see that continue, if not increase, in 2018.”

Northam and the Coalition to Stop Gun Violence endorsed state Sen. Jennifer T. Wexton (D-Loudoun), the most well known in the primary field.

Most Virginians — 91 percent — support requiring background checks for all gun buyers, according to a June Quinnipiac University poll. That survey found 51 percent support stricter gun laws overall and that 48 percent said it’s too easy to buy a gun in Virginia.

Independent analysts consider Comstock one of the most vulnerable incumbents in the nation, but she remains steadfast in her opposition to tighter gun laws.

While she has at times broken with Republican orthodoxy and President Trump, she has an “A” rating from the National Rifle Association and ranks 10th among House members who have received the most in donations from the NRA, which is headquartered outside the 10th District in Fairfax County.

The Democrats running for the chance to unseat her, meanwhile, hold nearly identical positions on guns, and each has been named a “candidate of distinction” by Moms Demand Action, an offshoot of the advocacy group Everytown for Gun Safety. They all favor background checks for every gun purchase, including private sales at gun shows and online.

Helmer has repeatedly criticized Wexton, the establishment favorite and the only elected official in the primary field, for voting for a 2016 legislative deal that expanded the rights of concealed-carry handgun permit owners in Virginia and around the country.

The bill was part of a compromise brokered by then-Gov. Terry McAuliffe (D), GOP lawmakers and the National Rifle Association that also forced some domestic abusers to relinquish their firearms and allowed voluntary background checks at gun shows.

But according to data from the Virginia State Police Firearms Transaction Center, few private sellers have voluntarily required background checks.

In 2016, state police conducted 39 background checks on private sales at gun shows. The number was down to 30 in 2017 but was already up to 30 in the first three months of 2018.

The numbers are a tiny fraction of the 41,919 background checks conducted at gun shows statewide in 2016, the 35,267 in 2017 and the 10,617 in the first three months of 2018, data shows. There are no records to indicate how many private sales were conducted without background checks.

While the Coalition to Stop Gun Violence denounced the concealed-carry aspect of the deal at the time, it has endorsed Wexton because she has supported and carried bills that would make it harder for perpetrators of domestic violence to have guns and would require background checks for private sales at gun shows. The stand-alone legislation has gone nowhere in the GOP-controlled General Assembly.

In his video, Helmer repeatedly asks the seller if he needs to undergo a background check or provide a Social Security number to buy the gun. The seller asks, “Are you a felon?” When Helmer responds “no,” a bystander laughs.

Helmer says that Wexton’s vote on the compromise gun legislation did not bring Virginia closer to requiring background checks on all sales at gun shows.

In response, Wexton’s campaign manager, Ray Rieling, said, “Senator Wexton is the one candidate in this race who has actually passed legislation making it harder to get a gun and carried legislation to close the gun show loophole.”

After buying the semiautomatic rifle for about $900, Helmer said, he altered it to stop it from firing and plans to turn it in to a police station that will not resell it.

Scott Clement contributed to this report.