As long as the US abuts a far poorer nation, some Americans will dream of a wall. The principle was established before Donald Trump ever became president.
Out in the scrub of Cormac McCarthy country, fencing already fortifies hundreds of miles of the Mexico border. Unless, like a bridge, it somehow stretches in the heat, Mr Trump needs funding from a reluctant Congress to fill in the rest. Perhaps he will succeed. More likely, legislators will deny him. Either way, he can but build on a structure that comfortably predates him.
The president’s defining policy does not quite merit its extraordinary shock value, then. Yes, there is something novel in the foulness of his anti-migrant rhetoric. The excesses of border enforcement also seem to be worse under his watch. But a physical barrier against Mexico is nothing new. In a more functional Washington, Democrats might even support its completion in return for kinder treatment of undocumented residents.