A single-payer health-insurance system can finance good-quality coverage for all U.S. residents while still reducing overall health-care spending by roughly 10%, according to a study I co-authored last November. All Americans would be able to get care from their chosen providers without having to pay premiums, deductibles or copayments.

Other countries currently provide good health care to residents at a fraction of the U.S. cost. As of 2017, the U.S. spent $3.3 trillion on health care—17% of gross domestic product. Germany,...