“Mexican government is going to write the US government a check for the cost of constructing a fence and securing its southern border.”
If they refused, that would be a perfect casus belli. We could establish a depopulated zone from the border down, say, to Mexico City.
That way they’d have to walk hundreds of miles if they wanted to die on the fence.
Well, I don’t really want a war with Mexico. I would be content to stop the flow of illegals, secure our borders, and enforce existing laws.