The southern border.

The drug war is an abject failure, and it's hurting African Americans and Mexicans far more than middle class white americans. In Mexico, drug traffickers bring American guns back into Mexico and are the murder rate along the border is up to several people per day. Much like the prohibition of alcohol lead to powerful and extremely hardy mafia families, the prohibition of cannabis has lead to the creation of extremely well-armed and well-organized drug cartels.

Some 95% of the guns used by these cartels in mexico have been linked to the united states, and obviously around 100% of their funding comes from the US. This influx of illegal money has corrupted officials as high as the cabinet level in the mexican government, and police chiefs country wide are either corrupt or in extreme danger.