As enacted, the ACA broadened Medicaid’s role, making it the base for coverage of nearly all low-income Americans with incomes up to 138 percent of poverty ($16,242 per year for an individual in 2015). However, the Supreme Court ruling on the ACA effectively made the Medicaid expansion optional for states.

So, doesn't the ACA provide for medicaid expansion,  as evidenced by over half of the states adopting medicaid expansion, including nearly all rust belt states and some red states as well?