That candidate is caught up in the very specific idea of "legal" and "documented alien" for methods of immigration without realizing that the racism inherent in the system will make it virtually impossible for anyone to meet legal qualifications for entry. Often the racism is hidden in the unwritten parts like the fees required to submit paperwork and the pressure for legal representation - all things that cost money and is designed to keep our the poors.
That candidate has no idea what nuance means and will run things like a tyrant, confused by a lack of clear morality.