They're not gonna use it as a prison. They're going to use it as a toehold to try and intimidate San Francisco with a standing military presence on the island. Don't get me wrong - they will imprison people there, but it's about getting a base for ICE right outside the loudest sanctuary city in the nation.

Alcatraz was built as a military fort and lighthouse, designed to control all maritime traffic into and out of the Golden Gate, long before it was used as a federal prison. That's what's really going on - they're making sure they have control of the second largest port on the West Coast.