We have had two wars with Mexico not counting the wars with the cartels. Perhaps what President Trump should do on Saturday, January 21 is to state that we are in a state of war with Mexico because of the cartels and the invasion of illegals.
On Monday, January 23 he should ask Congress to declare war on Mexico and then while Congress debates the issue authorize the 3rd Armored Corps from Fort Bliss to head south with orders to destroy the Mexican Army and the Mexican Federales and then to capture Mexico City. After Mexico City is secured, the rest of the US Army should head south to the Mexico-Guatamala and the Mexico-Belize borders and have the Army Corps of Engineers build the wall there.
Park a carrier on the east coast and west coast of Mexico, and take their oil as reparations.