A wall is an arbitrary border on either side of which are human beings. Its function is largely symbolic, to suggest that those on one side of the wall are somehow different from and inferior to those on the other. In this case the idea is that Mexicans feel themselves excluded from America, and Americans can rest in their beds secure in the knowledge they're better than Mexicans. Only...they don't need to. Already, Trump's frequent and confused pronouncements on immigration have resulted in increased attacks by godfearing white Americans on people of brown and black hue. And the consequence of that in turn is a drop in the number of Mexicans aspiring to live in America. For some reason the idea of earning poverty wages for jobs Americans show no interest in doing is even less appealing when that labour comes with a side order of toxic beliefs and occasional violence. In 1962 JFK made a speech which took America to the Moon by the end of that decade. That was about hope and collective endeavour and a vision not just of America but of mankind. In 2017, all Trump has to offer is the prospect of a wall which keeps away from him exctaly those people who were working on his various enterprises, since the man famously doesn't like to treat contractors fairly. If all the American president has to offer the world in the 21st century is a wall to confirm his prejudices and keep at bay some of those he owes money to, then that wall will be symbolic of a shameful period of US history, the symbolic act of an old man struggling for an erection at any cost.