Final answer:
The Supreme Court upheld the Affordable Care Act in National Federation of Independent Business v. Sebelius due to Congress's power to tax, but Texas has challenged the ACA because the 2017 tax cuts nullified the individual mandate's penalty.
Step-by-step explanation:
The Supreme Court in National Federation of Independent Business v. Sebelius held that the Affordable Care Act (ACA) was constitutional because of the power to tax, but Texas has sought to strike down the ACA in federal courts ever since the 2017 tax cuts eliminated the individual mandate requirement that had penalized Americans with no insurance coverage.
The individual mandate was a key provision that required all Americans to purchase health insurance or else pay a penalty, effectively a tax, which the Supreme Court deemed within Congress's power. However, after the mandate's penalty was reduced to zero by the Tax Cuts and Jobs Act of 2017, Texas and other plaintiffs argued that without the penalty, the individual mandate could no longer be considered a tax, thereby rendering the entire ACA unconstitutional. While the Supreme Court originally upheld the ACA as an exercise of Congress's taxing power, subsequent challenges to the law have arisen based on the changes enacted by the tax cuts.