The US spends ~$1.1T/year on Medicare today. US health care spending is estimated to continue rising and will reach nearly $6T a year by 2027. That means according to the federal government, the US will spend around $42.9T on health care over the next decade if we maintain the status quo. A recent study by Yale epidemiologists found that Medicare for All would save around 68k lives a year while reducing U.S. health care spending by around 13%, or $450B a year.
(for comparison, the DoD consumes ~$1T of spending, and debt interest costs ~$867B, annually as of this comment)
So the entire defense budget would not cover it.