Obamacare lives.

The U.S. Supreme Court today voted 5-4 to uphold all parts of the Patient Protection and Affordable Care Act, also known as ACA, also known as Obamacare. Against expectations and party lines, Chief Justice John Roberts joined the majority, with perennial swing vote Anthony Kennedy writing for the dissent. Roberts sided with the Court’s four liberal justices, ruling that Congress had not exceeded its constitutionally-mandated powers in requiring Americans to buy health insurance.

Interestingly, the ruling stipulates that Congress has the authority to impose the law’s individual mandate provision under Congress’s taxing powers, but not, as had been argued previously by the Obama administration, under either the Commerce Clause, or the Necessary and Proper Clause (though they had also made the tax argument as well).

It seems that the ACA would not have been upheld solely on the basis of the Commerce Clause alone (that Congress could use its power to regulate commerce between the states to require everyone to buy health insurance) – there simply weren’t the votes. It has been able to pass with the votes of five justices, however, because they ruled that the penalty someone must pay if they refuse to buy health insurance is in fact a kind of tax that Congress can impose through its taxing power. Congress has a specific power vis-à-vis the ACA – the power to tax. As the individual mandate survived, the whole statute was able to stand (apart from a little niggle about Medicaid and state compliance). The constitutional scholar Jack M. Balkin had a fine piece in the May edition of the Atlantic magazine presciently arguing that the healthcare mandate was clearly a tax, and therefore constitutional.

The decision – I think we can call it historic – means that thirty million hitherto uninsured Americans will now get healthcare coverage, and many millions will receive better insurance than they once had, whether it be extended drug coverage for the elderly, or the right to appeal against insurer treatment decisions from those who have to pay for said insurance. Really for the first time in U.S. history, millions of Americans will now always have the option of comprehensive healthcare coverage available to them.

Politically, the ruling is unlikely to change things much; if anything, it was an affirmation of the status quo, rather than a dramatic upturning of it. Republican voters may well be galvanised to turn out in droves come November’s general election. Speaker of the House John Boehner has already tweeted that “Today’s ruling by the Supreme Court underscores the urgency of #fullrepeal.” That’s a position you can expect to be repeated throughout the campaign, a Republican insistence that Obamacare must be repealed in its entirety. Democrats will be happy with the ruling, although they must guard against complacency. More broadly, today’s vote could have important long-term implications for the size and scope of the federal government.

The upholding of the ACA will be one of the key issues of the election campaign. Where President Obama and Mitt Romney are in fact very similar in any number of areas, Obamacare presents a wonderfully stark and binary choice to voters – keep it, or repeal it. We know Romney wants to repeal it, but what happens afterwards? Does he simply wish to return to a pre-Obama status quo? The ruling will shore up his core vote, but he needs his own healthcare policy, whatever that may be, to persuade independents to come into the red camp. Healthcare – which will soon account for fully one-fifth of the American economy – is far too important an issue to be dodged. But at least now the air has been cleared. The stakes are enormous, and only an election can settle the matter.