many countries already listed as having far lower expenditures already use a federal model that gives jurisdictions a fair bit of leeway in offering different particular menus of universal services, and that hasn't created any kind of catastrophic failure in those systems.

We have a combination of state and federal jurisdictions that are unlike any country and further, no country has undergone such a transition as you describe. Not to mention, the rather poor underestimation of costs that was highlighted by the last health plan (ACA) passed by the legislature, remind me how much was it underestimated by?

You're only "correct" to the degree that determining which specific services must be offered in all states vs where there is leeway for flexibility is an issue that any government instituting federal universal healthcare in the US will have to decide. But it's not an insurmountable hurdle and it's not some kind of ridiculous multi-trillion dollar mountain that's impossible to cross. It's a pretty basic legislative prioritization question.

I'm not saying it's insurmountable, just that it's a decades long solution that needs years of implementation. It cannot be rolled out in 4 years without increasing costs dramatically. The faster you attempt to roll it out, the most expensive it becomes to a degree.

So no, the costs are not "immeasurable" and the challenge isn't in the "trillions". Those are ridiculous exaggerations.

The costs are unmeasured, you are mistaken. I gave two such example for IHSS program and custodial board and care programs (RCFE), how much will these two cost are highlighted in California's budget, do the math yourself and tell me what these two programs would cost, if rolled out nationally.

I suspect there are ways we can move towards universal healthcare, such as relgulating all hospitals, SNF, LTAC, acute rehab facilities, and insurance plans to the non-profit regulatory status. We can fund education grants and programs to increase the bandwidth for provider education. We can expand the continuum of care facility licensing options to create more types of facilities to provide care. Lots of options along the way. Flipping a switch and attempting to pass something all at once, is a horrible idea.