And what "due process" are they owed in your view? They either have proof of citizenship or they do not. If they do not, then they are criminals by definition.
They are not owed anything, but the government has limits imposed on it by the Constitution. One of those limitations is due process before limiting someone's life or liberty.
Deportation is one thing; shipping directly to a prison in El Salvador is something else entirely.
Deportation is one thing; shipping directly to a prison in El Salvador is something else entirely.