In a little-noticed outcome of President Obama’s Affordable Care Act, jails and prisons around the country are beginning to sign up inmates for health insurance under the law, taking advantage of the expansion of Medicaid that allows states to extend coverage to single and childless adults — a major part of the prison population. State and counties are enrolling inmates for two main reasons. Although Medicaid does not cover standard health care for inmates, it can pay for their hospital stays beyond 24 hours — meaning states can transfer millions of dollars of obligations to the federal government. But the...