Cartels can maneuver past checkpoints  The current 650 miles of wall has done nothing to stop the flow of drugs. Cartels heavily study checkpoints and find their weaknesses and exploit them. Checkpoint officers can also be corrupted and/or ineffective. Most drugs also come through ports of entry, not the border according to the Institute for Policy Studies. Drugs is the biggest danger that comes from the free flow between the borders, yet a wall would not effectively stop the flow of drugs. If it does not stop the bringing of drugs into the US then the wall does not fulfill its purpose.