Ro Khanna, a Democratic representative, will introduce legislation Friday that lets states bundle all their health care spending — including Medicare, Medicaid, Affordable Care Act dollars and more — to fund a state-level single-payer system.

The policy could create something akin to Medicaid for all. It would be 50 separate programs, jointly funded by the state and the federal government, with local officials making decisions about whom to cover, how much to pay doctors, and what benefits to cover…

“The ideal would be that we have a full country with single-payer,” Mr. Khanna said. “That is what I think either a Sanders or Warren administration would produce. But in the absence of that, it’s preferable that we have some models of a single-payer system succeeding rather than no model at all.”

What he envisions is similar to Canada’s progression toward universal coverage. It began with a single province, Saskatchewan, which started hospital insurance in 1947. Other provinces followed, and within two decades, the entire country had government-provided health coverage.