Article I, Section 8, Clause I of the Constitution states:
"Congress shall have the Power to lay and collect Taxes, Duties, Imposts and Excises, to pay the debts and provide for the common Defense and general Welfare of the United States; but all Duties, Imposts and Excises shall be uniform throughout the United States."
Under the Taxing and Spending Clause, Congress has the direct power to tax while there is an implicit power to spend the revenue garnered from taxation. The extent to which Congress has the implicit power to spend has long been part of a contentious debate among scholars.
One of the major cases regarding the implicit right to spend is South Dakota v. Dole. Congress passed the National Minimum Drinking Age Act which required states to maintain a legal alcohol purchase age of 21 or lose part of its federal highway funding. South Dakota had set its age for purchasing alcohol at 19 and thus, decided to sue. South Dakota claimed that Congress overstepped its power under the Taxing and Spending Clause and justified the right of the states to regulate purchases of alcohol under the 21st Amendment of the Constitution. The Supreme Court rejected South Dakota's claims and upheld the law as appropriate under the Taxing and Spending Clause.
The 2012 case National Federation of Independent Business v. Sebelius was decided based on the Taxing and Spending Clause. The National Federation of Independent Business (NFIB) argued that the Affordable Care Act's individual mandate was unconstitutional under Congress's power to regulate interstate commerce. The Supreme Court agreed and disagreed on NFIB's argument. The Supreme Court agreed that the individual mandate didn't constitute as interstate commerce that Congress could regulate. However, the Supreme Court also agreed that the individual mandate could be upheld under Congress's Taxing and Spending Clause.
The Supreme Court had five conservative-leaning justices at the time but still voted to uphold the Affordable Care Act by one vote cast by Chief Justice John Roberts. Justice Roberts most likely voted to uphold the individual mandate because striking it down would have been viewed as a political move and could have tarnished the reputation of the Supreme Court. The 2000 case Bush v. Gore, which ordered the Florida presidential election recount to be stopped, was viewed as a purely political decision and had already tarnished the reputation of the Supreme Court. Through NFIB v. Sebelius, the Taxing and Spending Clause garnered a new power by allowing for an individual mandate.