The U.S. already has a system of free healthcare for the extremely poor called Medicaid.

I would not use Medicaid as a model, because it adds 50 state administrative overheads, on top of the Federal administrative overhead.

I would start with Medicare. Other countries have done the heavy lifting, to find out what works. Find the best practices, and adopt them to Medicare. If what the net sifter keeps coming up with is accurate, docs in the US would move to preferring Medicare patients, because of the lack of administrative overhead, and fast payment. Find out why the level of fraud in other countries is so low, compared to the US too. Then start phasing in Medicare availability to progressively younger cohorts. Paying for it would be the tricky part. If you charge premiums to the under 65s that enroll, if the premiums represent the cost structure, they should be lower than what people pay under the ACA now, because the administrative overhead and insurance company skim are not a factor. Employers would be offered the choice of offering Medicare as their employee health insurance benefit. Eventually, the private insurance companies would wither due to their administrative overhead and corruption, because no-one wants to deal with them. Once the majority of people are on Medicare, then shift to a tax supported model, and fold in Medicaid.

Steve