As Hillary Clinton seeks to beat back a surprisingly fierce challenge on the left from Bernie Sanders in the contest for the Democratic presidential nomination, the former secretary of state is calling out her rival on one subject where his votes suggest he is out of step with progressive thought: gun regulations.

Clinton has increasingly blasted Sanders over his vote for a 2005 law that grants gun sellers broad immunity from liability lawsuits. On Monday, at a campaign rally in New York, she asserted again that Sanders’s vote in favor of the Protection of Lawful Commerce in Arms Act, or PLCAA, is evidence that her opponent is not sufficiently tough on gun violence. Accompanied by family members of people who were killed in mass shootings in recent years, Clinton said that she refused to accept Sanders’s past explanations that his votes reflected the values of his rural-state constituency, which is generally more pro-gun than those in urban areas.

“Most of the guns that are used in crimes and violence and killings in New York come from out of state,” Clinton said, according to Politico. “And the state that has the highest per capita number of those guns that end up committing crimes in New York come from Vermont.”

Though Sanders said earlier this year that he would sponsor a bill to repeal PLCAA, he has remained committed to some of its core provisions. In a conversation with the New York Daily News editorial board earlier this month, the Vermont senator said he didn’t believe victims of gun violence should be able to sue firearms manufacturers or dealers for misuse of legally sold products. Sanders told the Daily News that he believes there should be an exception for when gun companies or sellers “should know that guns are going into the hands of wrong people.”

Sanders’s statements come as a lawsuit by the families of some Sandy Hook victims against Bushmaster, the company that made the gun Adam Lanza used to massacre schoolchildren and teachers in 2012, slowly makes its way through the courts. The lawsuit asserts that Bushmaster is liable because it marketed the gun as a killing machine, not for any lawful purpose.

Tension over PLCAA grew after a CBS reporter asked Sanders if he would apologize to the families of Sandy Hook victims. Sanders responded that he’d apologize when Clinton did so to the families of those killed in the Iraq war, which she voted to authorize. Clinton hit back, tweeting that Sanders “prioritized gun manufacturers’ rights over the parents of the children killed at Sandy Hook.”

The Trace has reported extensively on PLCAA, the law at the center of the dispute, as well as on the Bushmaster lawsuit that seeks to find a way around it. Here’s how the controversial law came about, and why Clinton has made such an issue of it.

Where did PLCAA come from?

In 1999, Bridgeport, Connecticut, sued two dozen gunmakers and sellers, along with three trade associations, claiming that the gun industry was negligent in failing to stop the flow of firearms to criminals. The lawsuit sought $100 million in damages.

Other cities soon followed, with the expectation that the legal pressure might force the gun industry to change its behavior in ways legislation had failed to do. Specifically, municipalities wanted to push gunmakers to stop doing business with unscrupulous dealers and invest in technologies like smart guns that prevent gun theft or criminal misuse.

Gun advocates fought back, mounting a successful defense in many of the lawsuits by arguing that firearms companies shouldn’t be liable for what a third party does with a gun — no more than an automaker should be responsible if someone drives drunk and causes a fatal accident. The industry also pushed for legislation to ward off future litigation, an effort that evolved into PLCAA. “Imposing liability on an entire industry for harm that is solely caused by others is an abuse of the legal system,” a key section of the legislation reads.

PLCAA has stopped most, but not all, gun business lawsuits.

PLCAA stopped the wave of lawsuits filed by cities, but individuals affected by gun violence have continued to sue gun shops, especially in instances where they claim the buyer’s behavior was suspicious, and should have served as grounds to stop a sale. These lawsuits have had mixed results.

Lonnie and Sandy Phillips, whose daughter Jessica was killed in the 2012 Aurora, Colorado, movie theater shooting, sued the website Lucky Gunner, which sold the gunman many thousands of rounds of ammunition. The Phillipses alleged that the online retailer lacked safeguards to prevent dangerous people from acquiring large quantities of weapons or ammunition. Sanders told the Daily News that he supports lawsuits like these: “If somebody walks in and says, ‘I’d like 10,000 rounds of ammunition,’ you know, well, you might be suspicious about that. So I think there are grounds for those suits.” The Phillipses’ lawsuit was dismissed on the grounds that PLCAA protected Lucky Gunner, and the parents were forced to pay the store’s legal bills.

Others attempts to skirt PLCAA have been more successful: In October, two Milwaukee police officers won a landmark $5 million judgement against Badger Guns, which sold a handgun to an obvious straw purchaser — a person who is legally allowed to buy a weapon and does so for someone who is barred from purchasing a gun. The straw purchaser soon turned the gun over to a convicted felon who shot and severely injured the officers.

The Badger Guns case was different from other attempts to sue gun companies because it was based on a proven instance of criminal misbehavior — straw purchasing — rather than harm that resulted from a potentially suspicious, but otherwise legal, sale.

Sanders says his Vermont roots, and concerns about the ramifications of unfettered lawsuits, influenced his gun votes.

Sanders has explained his vote for PLCAA by citing his state’s rural character. He represents Vermont, where guns are extremely popular. Appearing on NBC’s “Meet The Press” last July, he told Chuck Todd that “guns mean different things” to his constituents than they do in the urbanized states that have lead the charge for more stringent gun laws.

He has also cast PLCAA as a necessary protection for embattled small businesses. He has said that he wants to protect local “mom and pop” gun shops that might be put out of business if a gun they sold in a legal transaction was used in a crime. It’s an explanation that jibes with his populist message.

He has seemed increasingly defensive when pushed on the issue. At a March debate, Sanders argued that people who want to make it easier to sue gun businesses might as well be “saying let’s end gun manufacturing in America. That’s the implications of that, and I don’t agree with that.”

The political logic of Clinton’s attacks on Sanders’s PLCAA vote

Clinton is trying to use Sanders’s backing of PLCAA to stem his momentum, as he’s won eight of the last nine state nominating contests. Democratic strategists say they believe that coming out strong for gun control will motivate the voters who elected President Obama, much as the fight for marriage equality did in 2012. They say the NRA’s unwillingness to consider supporting any new gun restrictions in the face of mass shootings and persistent everyday gun violence has made the gun group into an ideal villain — one that Clinton has gone after with gusto.

Sanders’s voting record, and his attempts to reconcile his support for lawsuits against negligent sellers with his concerns about opening the floodgates to a wave of gun industry legislation, has provided Clinton with an opening.

“That’s a big difference between me and my opponent,” she said at Brown Memorial Baptist Church in Brooklyn on April 3. “He has voted with the National Rifle Association and the big gun lobby.”

[Photo: AP Photo/Carlos Osorio]