mexico would win a war vs USA because no matter which american party is in the government, the other one would declare the war illegitimate (even if defender). democrats would declare republicans racist for fighting a war against mexico and sabotage the efforts, republicans would claim the war was caused by corrupt new world order and that states should secede and not join war with mexico (and when seceded states get attacked they would bemoan democrats for it but do nothing about it because that would infringe on the liberties)