There’s a very tedious relationship. The US has sent troops to train the Mexican national police to combat the cartels, and helped provide weapons to the Mexican federal government. The US has sent money to the Mexican government to assist with that.
The issue is that corruption goes very high, and the cartels pay more than the Mexican Feds, so many of those trained took their training and weapons to the cartels, or just actively work with them as police on the side.
The US has tried, but without a strong federal government in Mexico that can deal with the root issues locally, there’s no real answer. If they can’t pay more than the cartels and get people to actually fight for their own lands, then they will never ever be able to build a force that can rival them for control. People the do bring in will either be killed because the cartels have inside players and more resources, or they will defect to the cartels and take the money and training with them.