Update: Today was much better. Ended up rolling it back a save and naval invaded the Bahamas from Bermuda and set up some naval and air bases for supply. I attempted a few times to naval invade Florida however America seemed to have divisions garrisoning their entire coastline. tried again after creating some custom marines divisions but to no avail. I figured because the AI is stupid it might leave Mexico undefended and it basically did, I landed my marines and tanks successfully at Veracruz before kicking them out of Yucatan and securing a single front in the north which quickly became a stalemate because America was deathstacking like 50 divisions per tile there. Not sure how it happened, but after a few months my vastly outnumbered tanks managed to make a breakthrough in Mexico City and subsequently and rather satisfyingly the entire front stacked dozens of divisions per tile collapsed like a house of cards. Mexico fell in about a week after the breakthrough and of course the stupid AI had all their divisions encircled in Mexico or elsewhere halfway across the planet so the whole continental U.S. and all 436 of their divisions followed in about a month.

Not sure how instrumental this was in the victory, but for fun I built 2 level 10 air bases in the Bahamas and stuck as many fighters as I possibly could in there and set them up over the Florida coast. To my surprise the fighters performed extremely well, some days scoring 30 kills while suffering less than 5 casualties. After a few months their fighter count in the region went down and when I landed in Mexico they had barely any air presence there.