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.

I didn't choose my words carefully enough. It's not a government run healthcare system that we're talking about, with government owned hospitals and clinics and all doctors etc. on the government payroll. Medicare for All is a single payer system, and it's not only possible but it would significantly reduce the overall national cost of health care. The transition would not be easy, with deeply ingrained interests and highly corrupt lobbying by those interests. But that shouldn't change the goal. The implementation would probably be gradual - starting with a drop in the Medicare eligibility age to 60, and perhaps also covering all children up to age 5, and then maybe closing the uninsured gap by another 10 years every couple of years. It's difficult, but it's possible and beneficial.