From SCOTUS Blog:
In Plain English: The Affordable Care Act,
including its individual mandate that virtually all Americans buy health
insurance, is constitutional. There were not five votes to uphold it
on the ground that Congress could use its power to regulate commerce
between the states to require everyone to buy health insurance.
However, five Justices agreed that the penalty that someone must pay if
he refuses to buy insurance is a kind of tax that Congress can impose
using its taxing power. That is all that matters. Because the mandate
survives, the Court did not need to decide what other parts of the
statute were constitutional, except for a provision that required states
to comply with new eligibility requirements for Medicaid or risk losing
their funding. On that question, the Court held that the provision is
constitutional as long as states would only lose new funds if they
didn't comply with the new requirements, rather than all of their
a majority of the Court has accepted the Administration's backup
argument that, as Roberts put it, "the mandate can be regarded as
establishing a condition -- not owning health insurance -- that triggers
a tax -- the required payment to IRS." Actually, this was the
Administration's second backup argument: first argument was Commerce
Clause, second was Necessary and Proper Clause, and third was as a tax.
The third argument won.