I don't perceive a reason to be concerned at all about this, as it's quite ambiguous and no indication there's a pending action. I consider it to be furthering pressuring the Mexican government to work with the U.S., and regain sovereignty of their nation, a good thing for both. That goes for other Latin American nations, as well. And Canada.
Cartels cannot be viewed simply as criminal groups; they are paramilitary organizations. Border security is national security; I think there are likely areas of opportunity for our military and border forces to cooperate.
It isn't just narcotics any more, if it ever was. Aside from human labor and sex trafficking, cartels are involved in a variety of cyber, finance, and extortion crimes. I'm skeptical legalizing would impact the cartels; why wouldn't they simply redirect their fortunes into newly-legalized drug cultivation and trafficking? The question is not whether we can eliminate crime and crime-fighting effort by legalizing an activity, but whether legalizing narcotics has any sort of net benefit. I don't see it.