A clever one, Chief Justice John Roberts.

While Roberts saved the Affordable Care Act and gave Democrats and liberals a big victory, he also gave Republicans and conservatives lasting weapons in their fight to rein in big government.

Most crucially, Roberts and the majority ruled that the supporters of the act couldn’t use the Commerce Clause to justify its constitutionality. The federal government can’t compel commerce.

“People, for reasons of their own, often fail to do things that would be good for them or good for society,” Roberts wrote in the majority opinion. “Those failures — joined with the similar failures of others — can readily have a substantial effect on interstate commerce. Under the government’s logic, that authorizes Congress to use its commerce power to compel citizens to act as the government would have them act. That is not the country the Framers of our Constitution envisioned....”

This marked the first time the court has put such a limiting principle on the Commerce Clause. Legal scholars quickly warned that a slew of other congressional and government actions could now face challenges based on Roberts’ opinion.

Score one for Justice Antonin Scalia and his fear that under the Commerce Clause the government could force everybody to buy broccoli.

Charles Fried, a conservative constitutional law professor at Harvard and solicitor general under President Ronald Reagan who thought the health care act was constitutional, told The New York Times that weakening the of the Commerce Clause “runs counter to 75 years of Supreme Court jurisprudence. It is a complete capitulation to the bogus logic of the broccoli argument....”

With the Commerce Clause disposed of, Roberts then determined that although the act called the enforcement mechanism of the individual insurance mandate a “penalty,” it was really a “tax.” (The act also called it a “shared responsibility payment.”)

Roberts’ argument gave the court’s dissenters fits. They charged that “the court today decides to save a statute Congress did not write.”

But Roberts said the penalty walks and talks like a tax.

“Congress can, of course, describe something as a penalty but direct that it nonetheless be treated as a tax,” he wrote. And under the constitution, Congress has taxing powers. So the mandate and the act stand.

Roberts seemed to think that recasting the individual mandate as merely a tax would make it more acceptable to Americans who don’t like being told outright what to do.

“Taxes that seek to influence conduct are nothing new,” he pointed out.

The key legal difference is that unlike a penalty, a tax is not a punishment for an illegal act.

“While the individual mandate clearly aims to induce the purchase of health insurance, it need not be read to declare that failing to do so is unlawful,” Roberts wrote. “Neither the act nor any other law attaches negative legal consequences to not buying health insurance, beyond requiring a payment to the IRS.”

Under this view, rather than forcing people to buy insurance, the act actually gives people a choice: Buying insurance is something government wants you to do, but you don’t have to. The choice is up to you.

Just pay the tax instead.

Still, while the tax dodge saved the act, Roberts could again be playing the long game.

For one thing, his opinion will make it more difficult for Congress to implement such a mandated penalty again without calling it a tax. In the future, such schemes would have to overcome America’s anti-tax inclinations.

Turning the penalty into a tax could also give Democrats some heartburn heading into the November elections.

Remember that Obama promised not to raise taxes on the poor and middle class. In a 2009 interview with ABC News, he debated host George Stephanopoulos over the dictionary definition of a tax and insisted that the mandate “is absolutely not a tax increase.”

Other Democrats also vigorously resisted calling the penalty a tax.

The Republicans will now be able to charge Obama and the Democrats with engineering a new tax and use that to fire up their supporters.

So a big battle is ahead for the Affordable Care Act. While the economy still figures to be the No. 1 issue in the election, the health care debate will harden the battle lines.

Roberts made clear that the future of health care should now be determined at the ballot box. In a passage that courts could apply to other contentious issues, he wrote in his opinion: “We do not consider whether the act embodies sound policies. That judgment is entrusted to the nation’s elected leaders.”

And therefore, its voters.

Vote for Obama and the Democrats and keep the act.

Or vote for Mitt Romney and Republicans and repeal it.

And all that would remain would be Roberts’ weakening of the Commerce Clause.

Pretty clever.