What about if instead of building the wall, America built...dug a two mile wide, one mile deep trench across its southern border with a series of canals to maintain current sea levels at the lips.
Used the earth they dug up to create new farming zones in say Utah and filled the new channel with water gained from the melting ice caps.
Should keep us at sea level and America could charge monies to use the new Trump cavity. Would save oil on Pacific to Atlantic runs too.