Vermont Senator Bernie Sanders may be gaining ground on Hillary Clinton in the upcoming Democratic presidential primaries by flanking her to the left, but he still needs to shore up his progressive bona fides on one issue: guns.

Sanders has been on the defensive when explaining his record of gun-friendly votes in Congress. He’s received the most grief for his support of the Protection of Lawful Commerce in Arms Act, or PLCAA, which granted gun businesses unique protection from civil liability.

Speaking with Fusion’s Jorge Ramos at a Democratic candidates’ forum earlier this week, Sanders explained his position on holding the gun industry accountable through his preferred framework: that of overweening corporate power. In the past he’s defended his vote for the bill as a way of protecting small gun stores, like those in his home state, from litigation that could drive them out of business. But he doesn’t extend the same consideration to gun manufacturers. As Sanders told Ramos: “If you are a gun manufacturer who is selling guns into an area and you’re selling a whole lot of guns, and you have reason to believe that a lot of those guns are not meant for people in that area, but are being distributed to criminal elements, should you be prosecuted? Damn right.”

There is a double irony to Sanders’s position, the first being that PLCAA eliminated the legal tools that would allow watchdogs to go after unlawful gun manufacturers. The law’s passage followed a series of lawsuits in the 1990s and early 2000s that targeted big companies such as Bushmaster for behavior like marketing guns that could serve no lawful purpose. While those lawsuits did not extract large settlements from gun makers, legal scholars felt they still had value because the discovery process sometimes uncovered evidence of dubious practices at private companies whose business strategy, operations, and financial records would otherwise remain shielded from government scrutiny.

One such revelation came in 2003, when a National Rifle Association executive forced to testify as part of a lawsuit brought by California municipalities admitted that the gun industry actively resists legislative efforts to prevent guns from being used in crimes. Once PLCAA was passed, plaintiffs like city or state governments couldn’t use negligence suits to learn whether gun makers knew more about how their products landed in the hands of criminals.

But even if that part of PLCAA were amended to clear the way for prosecutors to pursue negligence cases against firearms manufacturers, the Sanders approach would leave unchecked the part of the gun market most directly connected to, and vulnerable to, criminal activity.

Gun manufacturers distribute their products through local firearms dealers. Though legislation like the Tiahrt Amendments, which severely restrict how the ATF can share trace data, make it difficult to say with certainty how criminals get their guns, studies done before the ATF had its hands tied suggest that these intermediaries — the mom and pop shops Sanders says he’s trying to defend — are a common origin of guns for the black market.

According to a 2000 Bureau review of its trafficking cases, guns that were acquired from FFLs either through straw purchases, theft, or dealers illegally trafficking firearms themselves accounted for 68.7% of all investigations. A study of gun trafficking in the Los Angeles area from 1992 to 1995 found that dealers were the most common source of crime guns, either by selling to black market dealers or straight to criminals.

It’s more Sanders’s style to blame the big manufacturers. But the PLCAA law he helped pass makes it impossible to even begin establishing their responsibility. Meanwhile, it’s well established that local gun shops — whether due to negligence, deliberate misconduct, or the weak nature of gun laws — are a vital supplier to the illegal firearms market.

[Photo: Flickr user Gage Skidmore]