The only reason Mexico is even an issue is because the Mexican government does near to nothing to stop the flow of Criminal Aliens coming from El Salvador, Guatemala, and Honduras from coming across the U.S. border. As asylum law works internationally, asylum seekers must request asylum from the first country they enter. Therefore all asylum seekers leaving the "Latin Triangle" are to request asylum from Mexico.
As I have been saying for years, the U.S. has its troops in the wrong country. The reason the Mexican government does nothing is twofold -
1. Mexico lacks the funding to assist asylum seekers
2. The Mexican government has allowed the cartels to take over and the cartels are profiting of the illegal migration
The U.S. does not need a wall at its southern border. The U.S. needs to cease all financial aid to Mexico, El Salvador, Guatemala, and Honduras. A virtual wall made up of a U.S. military presence needs to be set up on the Mexican side of the border until the cartels are destroyed.