FIRST ON FOX — More than a dozen Republican attorneys general are defending American gun manufacturers against a lawsuit from Mexico that says the companies should be liable for gun violence south of the border, an argument that California and other Democrat-led states are supporting.

Mexico's lawsuit claims U.S. gun manufacturers like Smith & Wesson, Ruger and others are liable for gun violence south of the border because they are aware that their firearms are being trafficked into the country.

Mexico's lawsuit was dismissed by a federal judge in Massachusetts last year, but Mexico appealed its case to the U.S. Court of Appeals for the First Circuit, and the suit is supported by California and other Democrat-led states.

But this week, Montana Attorney General Austin Knudsen and 19 of his colleagues from other states argued in a legal brief that Mexico’s legal theory is "unsupported by fact or law."

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Attorney General Austin Knudsen

Montana Attorney General Austin Knudsen (Fox News)

"Firearms manufacturers are under attack from the Mexican government and anti-gun groups trying to bankrupt them for crimes they did not commit," Knudsen said in a statement to Fox News Digital.

"The court should do the right thing and affirm the district court’s decision to dismiss the suit. American companies cannot be blamed for problems in Mexico."

"On the facts, American gun manufacturers are not responsible for gun violence in Mexico," the AGs stated in a brief filed Thursday.

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"Rather, policy choices by the Mexican government, policy failures in the United States, and independent criminal actions by third parties are alone responsible for gun violence in Mexico.

"Mexico’s theory of liability rests entirely on the factual assertion that American gun manufacturers knowingly cause Mexican gun violence," the brief said. "But its theory falls apart under even cursory scrutiny.

"The available evidence suggests that gun violence in Mexico increased, not because of the expiration of the U.S. assault-weapons ban, but instead because of the Mexican government’s crackdown on the cartels.

guns ar-15

AR-15 style rifles are displayed for sale at a gun store. (REUTERS/Bing Guan/File Photo)

"Contrary to Mexico’s claims that American guns are ‘among the deadliest and most often recovered at crime scenes in Mexico,’ only a minority of guns recovered at crime scenes in Mexico can be traced back to the United States."

The brief said among the American guns recovered at crime scenes in Mexico, many were sold wholesale to the Mexican military and law enforcement and ended up in cartel hands after soldiers or police officers deserted them.

It said the age of the few American retail guns that do end up in cartel hands suggests that those weapons had been stolen or sold on the black market years after their legal sale in the U.S. and had not been intentionally trafficked to Mexico through straw purchases.

The AGs said Mexico claims that gun violence within its territory increased because of the expiration of the U.S. assault weapons ban in 2004. But their brief contends homicide rates in Mexico declined in the three years after the ban ended and didn’t increase until Mexico declared war on its drug cartels in late 2006.

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Mexico and California Democrat Attorney General Rob Bonta have argued that the Protection of Lawful Commerce in Arms Act (PLCAA), a law that protects gun companies from liability for "misuse of their products by others," should not apply in this case.

But Knudsen and his colleagues say this case is exactly why the statute is in place.

Guns on a shelf

Firearms are displayed at a gun shop in Salem, Ore., Feb. 19, 2021.  (AP Photo/Andrew Selsky, File)

"Congress didn’t pass PLCAA in a vacuum. Instead, it did so in direct response to lawsuits from anti-gun groups seeking to financially cripple the firearms market — just as Mexico does here," their brief said.

"Before PLCAA’s enactment, no high court in the United States found gun manufacturers liable for the criminal acts of third parties."

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"PLCAA simply codified this existing causation standard to protect gun manufacturers from the expense of litigating meritless tort cases and from tort law innovations targeting the gun industry," they stated.

States signing on to the brief include Alabama, Alaska, Arkansas, Florida, Georgia, Indiana, Iowa, Kentucky, Louisiana, Mississippi, Missouri, New Hampshire, South Carolina, South Dakota, Texas, Utah, Virginia, West Virginia and Wyoming.