This main answer is well known, though it's always helpful to see the current state of things reported. Noting that Mexico is currently experiencing "unprecedented levels of gun violence, which have claimed more than 100,000 lives over the last decade," Linthicum explains:
Last year was Mexico's deadliest since the government began releasing homicide statistics in 1997. This year, it is on track to surpass that record.And she reports about a move by the Trump Administration apparently aimed at increasing this traffic criticized by gun-proliferation opponents:
American firearms are directly driving the violence, although U.S. appetites for drugs and rampant corruption among Mexican officials also play a role. About 70% of guns recovered by Mexican law enforcement officials from 2011 to 2016 were originally purchased from legal gun dealers in the United States, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives. ...
Most trafficked guns are purchased in the U.S. from one of the country's more than 67,000 licensed gun dealers or at gun shows, which unlike stores often do not require buyers to present identification or submit to background checks. [my emphasis]
They are also concerned about a new Trump administration proposal to deregulate the export of American guns by putting the Commerce Department in charge of the application process instead of the State Department, which advocates say is better suited to weigh the possible risks of firearm sales against any benefits.Sadly, that's a stereotypical example of the Democratic Party's approach. Propose something that makes practical sense, but try to keep it from attracting attention even though it is consistent with the popular attitude demanding better gun regulation, in this case. Intensity gap with the Republicans? Lack of seriousness? Paid by their campaign donors to lose? Is there any practical difference in the results with any of those options?
The proposed rule change, which is expected to be published in the Federal Register on Thursday, has long been sought by gun companies eager for easier access to international markets, but advocates worry it could put more guns in the hands of corrupt governments.
U.S. Rep. Norma Torres (D-Pomona) introduced a bill that would limit the impact of such a change, as well as legislation that would make gun trafficking a federal crime, which it currently is not. Torres said she has not sought to draw attention to her work to stop arms trafficking because she is wary of pushback from gun industry groups such as the National Rifle Assn. [my emphasis]