Every other OECD country has universal government run healthcare. They all have lower costs and most of them have better outcomes. I don’t think any other proof is necessary that Medicare for All is possible.

Yes, you need other proof.

All of those countries have universal government run healthcare. None of them has tried to convert from a private health care system that has grown to 18% of GDP into a universal government run health care system.

Path dependence is a real thing. Having allowed our health care sector to grow to the current size, with decades of decisions based upon having a private system, it is no longer possible to switch. You would inflict too much economic harm on too many people for it to be politically feasible. You can't switch over unless you either: i) adopt levels of coverage lower than the typical large group employer plan; or ii) slash provider compensation; or iii) have massive, broad based increases in the amount that most people pay for health care either in premiums or taxes. All of those are political non-starters. The idea of single-payer health care might be popular, but because of where we are, the path to get there requires doing some very unpopular things. Which is why Vermont and California and other sapphire-blue states with progressive leadership have failed to make it happen.