The United Kingdom’s National Health Service, which celebrated its 70th anniversary on July 5, is imploding. Vacancies for doctor and nurse positions have reached all-time highs. Patients are facing interminable waits for care as a result. This August, a record number of Britons languished more than 12 hours in emergency rooms. In July, the share of cancer patients who waited more than two months to receive treatment soared. Yet enthusiasm for government-run, single-payer health care continues to build in the U.S. One look across the Atlantic, to the disaster unfolding in the U.K.’s government-run healthcare system, ought to curb that enthusiasm.