Whenever I write or talk about the 3-Legged Stool of the ACA and the actual flaws in the law (as opposed to the ones deliberately created by the GOP), I usually focus on two "gaps" in the legs: The APTC subsidies getting cut off at 400% FPL and being too stingy below that level, and the individual mandate not being large enough (and not being properly enforced). As it happens, part of the first problem has already been unintentionally "solved" thanks to Trump's ham-handed CSR reimbursement cut-off (which ended up increasing APTC tax credits for those below the 400% cut-off), while the second problem has just been made a whole lot worse thanks ot the GOP repealing the mandate altogether.
However, in focusing on the legs of the stool, I often forget to mention another important issue: The width of the seat itself. That is, how wide the network of doctors and hospitals which accept the policy is. The Affordable Care Act does give some guidelines/regulations about how wide ACA-compliant policy networks have to be, like so:
