The Supreme Court has upheld almost all of the big health-care law sometimes called Obamacare but actually titled the Patient Protection and Affordable Care Act.

A bare five-member majority consisting of Chief Justice John Roberts plus the court’s four liberals (Justices Stephen Breyer, Ruth Bader Ginsburg, Sonia Sotomayor  and Elena Kagan) ruled that the individual mandate, requiring everyone who can afford it to buy a health insurance policy, is constitutional.

But that oversimplifies the coalition that upheld the law. The liberals ruled that the creation of the mandate is acceptable as part of the federal power to regulate interstate commerce. Roberts disagreed on that point, but found that the mandate can be treated as a form of tax, and on that basis can be upheld.

Three conservatives – Justices Antonin Scalia, Clarence Thomas and Samuel Alito, plus the usual moderate swing vote – Anthony Kennedy – ruled that the mandate exceeds the power granted to the federal government under its power to regulate interstate commerce. And without the mandate, the rest of the law falls apart. So they voted to strike down the whole bill.

Obviously this is huge and has political, legal, constitutional, Supreme Court institutional and enormous health-policy dimensions.

It will take some time to figure out the details. If you want to read the ruling for yourself, it is here. (It comes in several portions and that file includes the dissent by the four justices who preferred to strike down the whole law.)

Roberts broke ranks with the four liberals on one important aspect of the law, but it will take a while to figure out the implications.

The law as passed significantly expanded eligibility for Medicaid, the health insurance program for the poor. Medicaid is a state-federal cost-sharing program. As written, the feds threatened to cut off federal Medicaid payments to states that refused to go along with the expansion. Roberts ruled that the feds cannot do that. States that want to opt out of the expansion of Medicaid can do so without being penalized by the withholding of federal funds elsewhere in the Medicaid program.

It will take a while to figure out the impact of this. Most Republican governors around the country are hostile to the overall law. Apparently, Roberts’ ruling gives them the authority to opt out of the Medicaid portion of the law without being cut off from the Medicaid program entirely. But if, in doing so, they would be foregoing federal assistance that would have enabled them to expand health insurance for some of their own poor citizens, it might not be that easy for them to turn it down.