Sanders’s bill, the Medicare for All Act of 2017, has no chance of passage in a Republican-run Congress. But after months of behind-the-scenes meetings and a public pressure campaign, the bill is already backed by most of the senators seen as likely 2020 Democratic candidates — if not by most senators facing tough reelection battles in 2018.

The bill would revolutionize America’s health-care system, replacing it with a public system that would be paid for by higher taxes. Everything from emergency surgery to prescription drugs, from mental health to eye care, would be covered, with no co-payments. Americans younger than 18 would immediately obtain “universal Medicare cards,” while Americans not currently eligible for Medicare would be phased into the program over four years. Employer-provided health care would be replaced, with the employers paying higher taxes but no longer on the hook for insurance.