The touchy debate over gun control is moving forward after President Obama said he would bring the issue before Congress in January, and whatever policymakers decide — if anything — could affect Mexican drug violence.

University of Massachusetts economist Arin Dube says the expiration of the U.S. assault weapons ban in 2004 put more powerful weapons into the hands of Mexican drug cartels.

“Within months of this change in policy we saw an uptick exactly where we would expect,” said Dube, who co-wrote a paper on border violence this year.

That uptick happened in Mexican towns near border states like Arizona and Texas. But the violence was not as prevalent near California where strict gun laws are still on the books, Dube said. Even before this week’s debate, gun advocates dismissed the role of U.S. gun policy in Mexico.

And Alejandro Hope, with the Mexican Institute for Competitiveness in Mexico City, said violence near the border has many sources.

“It has to do with the shape and structure of drug markets. It has to do with Mexican government policy,” Hope said.

He added the flow of guns to Mexico won’t do much to reduce the demand that drug cartels have for them.