Rebekah Stewart, a nurse at the U.S. Public Health Service, got a call last April that brought her to tears. She had been selected for deployment to the Trump administration’s new immigration detention operation at Guantánamo Bay, Cuba. This posting combined Donald Trump’s longtime passion to use the offshore base to move “some bad dudes” out of the United States with a promise made shortly after his inauguration last year to hold thousands of noncitizens there. The naval base is known for the torture and inhumane treatment of men suspected of terrorism in the wake of 9/11. “Deployments are typically...