In other words...we don’t have a border.
Back in the day, there really wasn’t much of a “border”.
It was just a fence.
It was really easy to identify The Americans: they were white, and spoke English. A few were black, and spoke English (kind of), but since there were no Mexican black people, everyone understood.
So when Mexicans came across illegally it was easy to identify them. They really did look like Emiliano Zapata and spoke “Spanish” with a snarl.
So we didn’t need a wall. Everyone knew who everyone else was.
Then they passed all the “civil rights” legislation and it became impossible to identify the “Americans” without “documentation”: Civic Nationalism took hold! ANYONE could be an American...they just hadn’t gotten here yet, and gotten their “papers”. Undocumented? No problemo! El Primero Mayorkas will print you up some documents right away! Presto! Ju are an Am-erik-an!
Thus we need a wall now to make sure that only the people with the “documents” get in. Cuz see...no one can identify the Americans anymore by sight and sound.
Which used to be the case. And why we only needed a fence.