I'll like to make a brief observation about Trump's proposal to build a wall to keep illegal aliens out. Presumably, the idea is to build a wall across the US-Mexico border.
There's one little logistical hitch: last time I checked, the USA was not a landlocked country. So Trump's wall would have to extend across the West Coast, Gulf Coast, and East Coast to seal our borders. The US shoreline is about 95,500 miles long. (The US-Mexico border is about 2000 miles.)
That presents some intriguing engineering challenges. To begin with, the wall has to be deep enough to reach the continental shelf.
In addition, a coastal seawall would completely impede fishing, shipping, naval operations, &c.
Furthermore, a border wall would dam the Colorado and Rio Grande Rivers.
Then there's the question of what to do about pesky illegals who try to sneak in through the northern border via Alaska. Admittedly, that's not a big deal right now, but if we wall off the East coast, West coast, Gulf coast, and US–Mexico border, that will make other points of entry more popular.
An alternative might be a build a geodesic dome or plexiglass dome over the continental US. Make the US a giant terrarium. Of course, that would eliminate international air transport, &c. But it's a small price to pay for sealing the border.