Do we enforce the Monroe Doctrine anymore?
Thank Obama for non-enforcement (per a lookup):
President Barack Obama's Secretary of State John Kerry told the Organization of American States in November 2013 that the "era of the Monroe Doctrine is over."
No we don’t. The other half of the Monroe Doctrine was that we don’t interfere in European affairs. People forget that part of the doctrine.
That's what I was thinking. One thing that was constant over the last two centuries, is that the US will not tolerate troops from a potential major-power adversary in the Americas.
Allowing a major adversary to establish a military beachhead where they can just drive to the US, creates a potential major threat. It was one of the premises of the original version of the movie "Red Dawn", where a communist coup in Mexico allows the Russians to use it as a staging area for invasion.