Boatloads of tourists traipsed around Alcatraz Island on Monday morning and peered into tiny prison cells, learning about the most notorious inmates who stayed there — and the ones who tried to escape.

The tour was standard at the revered San Francisco attraction, save for one topic that simply could not be avoided in the conversations echoing off the old cellblock walls.

Can you believe that President Trump wants to convert Alcatraz back into a federal prison?

The morning tour groups were full of international travelers, and many of them had received phone alerts about Trump’s plan or read news reports over breakfast. Some wondered if they might actually be among the last visitors allowed to wander the island. But nobody seemed to think the idea was nearly as brilliant as Mr. Trump thought it was.

“I thought it was a joke,” said Philipp Neumann, who was visiting from Germany. “It’s a ruin, isn’t it, more or less?”

A ruin, yes, with some buildings deteriorating so badly they no longer have roofs or complete walls. The cells have broken toilets, if they have any at all, with no running water or sewage system.

The exterior walls of the cellblocks are so weak that they are reinforced with netting to prevent chunks of concrete from crumbling onto tourists’ heads. Bird deposits coat much of the island. All supplies from food to fuel must be brought in by boat.