Latest realistic POD for a Mexican Central America?

Spanning from the Rio Grande to the border with Panama, is it possible to have Mexico take most of Central America after, say 1880? (excluding Belize)
Bonus: This may be a stretch but is it remotely possible with a POD in the 20th century?

Obviously, Central American countries are quite different to Mexico and I imagine it is probably unlikely that this could have been pulled off. But say all the stars are aligned in Mexico's favour, what is their best case scenario for expanding south in the late 19th century/early 20th century?
 
I think a late 19th early 20th c. POD is extremely unlikely because Mexico spent much of that time in economic and political turmoil, the Central American nations will resist militarily, and the US would strongly oppose them (probably militarily as well). Mexico had a hard time holding onto the Yucatan so expanding southward might be a stretch in that time period. The biggest obstacle definitely seems to be the US, who's going to want to counter any expansionist move Mexico makes and has the resources to do so.

I think this becomes much more plausible though with a POD in the post Mexican-American War period or earlier. A strong Mexico timeline would need increased stability, investment, and immigration (and probably more economic equality). Make Mexico richer and this becomes more plausible and with a stronger Mexico earlier on you also have less US interest and involvement in Central America. Basically if Mexico moves south in 1850-70 the US will care a lot less than if Mexico moves south in 1880-1900.
 
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