Final answer:
The Supreme Court upheld most of the ACA as a constitutional extension of Congress's power to tax in National Federation of Independent Business v. Sebelius. Further cases like King v. Burwell clarified aspects of the ACA's implementation, with the Court supporting the provision of federal tax credits for health insurance regardless of state or federal exchanges.
Step-by-step explanation:
The Supreme Court has played a pivotal role in establishing the constitutionality of the Patient Protection and Affordable Care Act (ACA), also known as Obamacare. In the landmark case of National Federation of Independent Business v. Sebelius, the Court was presented with a challenge against elements of the ACA, namely the individual mandate and Medicaid expansion. By a narrow decision of 5-4, the Supreme Court determined that while the federal government could not coerce states into expanding Medicaid by threatening to cut off existing funding, the individual mandate fell within the congressional power to tax, thereby upholding most of the ACA.
Subsequent rulings, such as King v. Burwell and Burwell v. Hobby Lobby, addressed specific provisions of the ACA, further shaping its implementation. Significantly, in King v. Burwell, by a decision of 6-3, the Court upheld the ability of the federal government to provide tax credits to individuals purchasing health insurance through federal exchanges, despite some ambiguity in the law's wording. These decisions have affirmed the ACA's legality while delineating its limits and reinforcing its intention to make health insurance more accessible to Americans.