Sorry that I wasn’t clear. Canada and United States of America joined as founding members of North Atlantic Treaty Organization. The organization allows only European countries to join after the founding date. Canada essentially gets grandfathered, but if Canada departs from the alliance, it cannot reenter (unless it acquires part of Europe). Mexico did not join as a founding member and therefore cannot enter (unless it acquires part of Europe).
The narcotics smugglers and sexual slavedrivers enter the United States of America through the southwestern border with Mexico as enemies of these United States and as enemies at war against the weak Mexican government and the Mexican people. The United Mexican States does not constitute a hostile enemy but fights a long-running war against that enemy within her borders. Just as the drug runners and urban gangs of Chicago do not define this country, the narcoterrorists do not define Mexico.
Instead, the United States and Mexico share a common enemy: the narcoterrorists, the drug cartels, and the bankrupt oppressive communist government of Bolivarian Republic of Venezuela that sponsors, supplies, and encourages them. This enemy now ravages much of Central America, driving repeated surges of refugees and other migrants northward toward our border.
I make a distinction between the Mexican government and the friendly Mexican people on the one hand and the narcoterrorists, sexual predators, transnational criminals, and drug cartels that operate in or from Mexico on the other hand. The latter group we must defeat.