The USA spends around 18% of its GDP on healthcare already, which larger than any other big country, the Netherlands is next on 12%.
Given the military spend is 4.7% of US GDP it is patently untrue that military spending means that more couldn't be spent on healthcare. You could have a healthcare system that is 50% better than any other Western country, for everyone, just by reallocating the money already spent on healthcare.
Yes, money != outcomes, but it works roughly. Especially as there is so much low hanging fruit in the USA due to the shocking state of healthcare provision for the poor.