North of the border, the .50-caliber sniper rifle is the stuff of YouTube celebrity. It is among the most destructive weapons legally available in the United States. But every week, those rifles are trafficked across the border to Mexico. After years of failed U.S. and Mexican efforts to curb arms trafficking, groups such as the Jalisco New Generation and Sinaloa cartels are showcasing the military-grade weapons in slick propaganda videos and using them to defeat security forces in battle. Roughly 2.5 million illicit American guns have poured across the border in the past decade, according to a new Mexican government study. The cartels are using trafficked weapons to kill record numbers of police officers 464 in the first nine months of 2020 alone " and smaller armed groups are fueling historically high homicide rates. Mexican officials, in rare public criticism, are now venting their frustration at what they say is the U.S. failure to stop the flow of .50-caliber rifles. At a time when the United States is pushing Mexico to target cartels more aggressively, U.S. laws that make .50-calibers and other destructive weapons easy to buy ... are enabling those groups to expand their influence and activities in the country. A decade after "Operation Fast and Furious," in which U.S. agents allowed thousands of firearms to flow south in a botched attempt to track them, and despite $3 billion in U.S. aid to Mexico to fight narco-traffickers, the two countries have not curbed the flow of weapons.