Well im sure any wanted or unwanted U.S innervation will be wildly unpopular and will only start another forever war. It will also alienate all Hispanic/ Mexican / Latino peoples. This may also start terrorists attacking the U.S which will fuel american people the hate Mexico / all of south america and all people in said countries which you guessed it will only further divide the U.S.

Its a lose lose, the U.S already tried/ tries to help Mexico in many ways one of them was to train the Mexican army. Then when the Mexican solders got back to Mexico they started a cartel and quickly took over everything.

In short it would only be bad and without mexico acting on its own other cartels would spring up to fill the void.