There are over 258 million adults in the US.
Let’s say all the 21.4 people who use the ACA exchanges get subsidies, to simplify things.
That’s 8.2 % of the adult population.
I don’t think that can account for Obamacare’s popularity, just as a matter of arithmetic.
Even if you include the Medicaid expansion, you’re still far from a majority of adults.
