The Trump administration’s Medicare chief is taking aim at a health coverage proposal gaining momentum among Democratic 2020 presidential hopefuls.

In what appeared to be a response to the heightened discussion surrounding “Medicare for All,” Centers of Medicare & Medicaid Services Administrator Seema Verma said “the reality is we can barely afford the program we have.”

One of every five dollars will go to health care by 2026 if action isn’t taken, Verma said, citing the CMS’s actuary predictions in a speech in Baltimore Jan. 29. The Affordable Care Act didn’t didn’t alter the “trajectory of health-care spending,” she said....