By John R. Lott, Jr.Author, "Freedomnomics"/Senior Research Scientist, University of Maryland

It is pretty hard to seriously argue that a new so-called "assault weapons" ban would reduce crime in the United States. Even research done for the Clinton Administration couldn't find that the federal assault weapons ban reduced crime.

There are no academic studies by economists or criminologist that find the original federal assault weapons ban reduced murder or violent crime generally. There is no evidence that the state assault weaponsbans reduced murder or violent crime rates --and there's even some evidence that they may have caused murder to actually rise slightly. Since the federal ban expired in September 2004, murder --and overall violent crime rates-- have remained virtually unchanged.

If Holder thinks that it is so easy to control drug gangs' access to guns, one way to show it is by proving that he can stop drug gangs' access to drugs.
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But yesterday, Attorney General Eric Holder offered a new justification: "I think that will have a positive impact in Mexico, at a minimum."

Mexico does have a horrible drug gang problem. Despite Mexico's strenuous efforts, they haven't been able to stop the flow of drugs into their country on their way to the United States.

The problem is that even if all our guns disappeared in the United States, there is no more reason to expect the flow of guns to Mexico to stop than there is to believe that we can stop the flow of drugs.

The drugs that these gangs sell are extremely valuable. They want to protect these drugs not only from the Mexican government but also from other gangs. Just as these gangs have a huge incentive to smuggle in guns, they have a huge incentive to smuggle in the guns used to protect them.

Even island nations -- such as Ireland, Jamaica, and the UK-- that can't remotely begin to blame their crime problems on the United States have seen large increases in murder rates after gun bans at least in part because of increased drug gang violence.

If Holder thinks that it is so easy to control drug gangs' access to guns, one way to show it is by proving that he can stop drug gangs' access to drugs. No one should hold their breath for him to accomplish that task.

John Lottis the author of Freedomnomicsand a senior research scientist at the University of Maryland. Click herefor an archive of Mr. Lott's previous FOXNews.com columns.

John R. Lott, Jr. is a columnist for FoxNews.com. He is an economist and was formerly chief economist at the United States Sentencing Commission. Lott is also a leading expert on guns and op-eds on that issue are done in conjunction with the Crime Prevention Research Center. He is the author of nine books including "More Guns, Less Crime." His latest book is "The War on Guns: Arming Yourself Against Gun Control Lies (August 1, 2016). Follow him on Twitter@johnrlottjr.