There isn't much doubt that much of the illegal drugs that enter America, come from our southern neighbor, Mexico, and to interdict such drugs from entering this country, America spends an inordinate amount of money on border control, border agents, border walls, and heavy security at border entry points, which slows border crossing traffic to a standstill. While, to a certain degree one could applaud the amount of drugs confiscated by the U.S. Customs and Border protection agency, of which, as reported by azcentral.com, "During the 2016 fiscal year, CBP agents seized 246,000 kilograms of marijuana, meth, cocaine and heroin at southwest ports of entry compared with 589,000 kilograms outside ports of entry;" this is mitigated by the very fact that significantly more drugs were seized outside ports of entry (e.g. outside vehicle ports of entry at border crossings); indicating, that drug cartels are quite skilled at crossing the border through the air, through the sea, through drones, through underground tunnels, and through remote ground crossings that are simply not patrolled.
The idea that by building a wall that is 2,000 miles long, and 30 feet high, with even more border patrol personnel, even more sophisticated monitoring devices, even more monies allocated, and so on, will somehow reduce the amount of drugs coming into the United States to something approaching zero, is simply delusional. For one, there is simply too much money involved in the illegal drug trafficking trade that affects both sides of the border, that such an amount of money would still have its corrupting influence in aiding and augmenting the trafficking of those narcotics. In addition, wars have proven time and time again, that the mere building of a wall, in and of itself, will not, provide absolute protection and an impenetrable defense, though it may well help, but to believe that such a wall, will simply stop business as usual, is deceit at its very worst.
Even the belief, that most illegal narcotics are simply being driven over the border, is fundamentally wrong, for drug traffickers, know for a certainty that border crossings, no matter the deception and sophistication involved are always going to be risky, as compared to an end-around such as tunneling under the border, flying a plane below radar detection, utilizing drones, utilizing sea containers on transport ships, finding areas of low patrol, or traveling by sea.
The fact that the United States, declared a war on drugs in 1971, and yet the drugs are still widely accessible in America and the drugs are yet still coming to America, indicates wholly that this war as being fought by the United States, noble or not, has failed, completely. This would indicate what far few people wish to actually discuss, which is that the border patrol for the most part are interdicting small-time players, whereas the big-time players are able to quite successfully export their drugs over to America, probably for a lot of reasons, of which one of the most salient ones, is that money greased and gifted to the right people in America will get business done; whereas more laws, more walls, and more border patrol agents, really won't.