A. It is not mandatory: https://en.wikipedia.org/wiki/National_Federation_of_Indepen...

B. https://en.wikipedia.org/wiki/Patient_Protection_and_Afforda...: "The federal government paid 100% of the cost of Medicaid eligibility expansion in participating states in 2014, 2015, and 2016; and will pay 95% in 2017, 94% in 2018, 93% in 2019, and 90% in 2020 and all subsequent years."