What you're saying is "Warren. It's her claim"
What I'm reading is "No, you".
Private Insurance replacement($9T) + Wealth and Large Corporation tax(~$6T/year) + Tax Enforcement($2.3T) = $17.3T
20.5 - 17.3 = 3.2T
Not really as far off as you thought, is it? Mix in immigration reform(great way to increase tax revenue), adjustments away from military spending, reduction in overhead, fewer bankruptcy and hospital losses, and reduction in out of pocket costs(co-pays, etc), and how close do you figure we get?