Possibly misattributed, but usually given to HL Mencken:
"For every problem, there is a solution that is simple, neat, and wrong."
Don't kid yourself into thinking a complex system that makes up 20% of GDP is going to have a simple solution. Just a couple examples you'd have to contend with:
1) Insurance companies get a say too, according to the Constitution. That means they get to lobby in their own interests. That political problem itself is a boondoggle.
2) The US funds a disproportionate amount of medical R&D. Some of that fat is going to be cut from research. You need to have a plan on how that will effect long term quality of care and innovation.
3) Physician licensures are limited by the AMA. If you expand coverage, you will need to expand supply because any time something becomes "free", people will consume more of it. That's not a necessarily bad thing in healthcare, but needs to be addressed. The AMA also gets to defend their political interests.
There's lots and lots of other issues. I'm not claiming the US healthcare system is great. But pretending it has a simple fix is naïve.