According to O3 US public health spending (state + federal) is 8.6% of gdp. For perspective, here's a list of countries with universal systems which spend less (these numbers include private spending), and life expectancy (US is 78.4 for reference):

  Singapore: 5.6%, 82.9
  Israel: 7.2%, 83.2
  Estonia: 6.9%, 78.5
  Poland: 6.7, 78.5
  Luxembourg: 5.7%, 83.4
  Czech Republic: 8.1%, 79.9

and a couple which spend a bit more, though again, this includes private spending:

  France: 11.9%, 82.9
  Japan: 11.5%, 84
  Portugal: 10.5%, 82.3
  Spain: 10.7%, 83.9

So it seems like we could have universal coverage and higher life expectancy if the US government simply spent exactly what it is currently spending, but on everyone, rather than just the old, poor, and veterans.