Earlier this month, Time magazine named President Obama its "Person of the Year." This wasn't surprising, given that the magazine has often given this distinction to the winner of the presidential election. But if I were to name a public figure who had the most influence in 2012, it would have to be John Roberts, chief justice of the United States Supreme Court.

When Roberts allied himself with liberal justices in June to uphold the constitutionality of Obama's national health care law -- even though he had the opportunity to join with conservative justices and overturn it -- it was one of the most significant Supreme Court decisions in history.

Justices shouldn't make decisions based on their policy preferences, of course. But Roberts' decision did have very important policy consequences.

In practical terms, Roberts helped enshrine one of the most sweeping laws ever enacted, which will affect Americans in the most personal of ways. The law increases spending by $1.7 trillion over the next decade and hikes taxes by $1 trillion. It imposes a raft of new regulations on businesses and requires individuals to purchase government-approved insurance policies. And in the long run, it expedites the day when America will become indistinguishable from a European-style welfare state.

But beyond the policy implications pertaining to this particular law, Roberts' decision to uphold the constitutionality of the law's individual mandate, to borrow a phrase from Justice Anthony Kennedy, fundamentally changes the relationship between the individual and the federal government.

Roberts did reject the central claim made by Obama administration lawyers, which was that the federal government had broad power under the Commerce Clause to impose an individual mandate to purchase health insurance. But he ultimately ruled that they could do so anyway as a result of their taxing power, because there is a fine attached to the failure to purchase health insurance.

Numerous reports indicated that Roberts originally was a vote to overturn the mandate but that he flipped. Some have argued that he did so to avoid criticism from elites that the court had become excessively partisan; others have claimed that it was because conservatives were pushing him to overturn the entire law rather than just the mandate, and he wasn't ready to go that far.

Whatever his motives, ruling the way he did required Roberts to rewrite the law. In the text of the legislation, the penalty for not purchasing insurance was not described as a tax; it did not appear in the section of the law pertaining to taxes; and it wasn't primarily intended to raise revenue, but to compel somebody to purchase a product. Nonetheless, Roberts decided it was operationally a tax on not buying insurance.

So, under the precedent of this ruling, the government in theory shouldn't be able to mandate that individuals take certain actions, nor will lawmakers be able to force Americans into a stream of commerce. But in practice, they will be able to mandate whatever they want as long as they attach a nominal fee to the mandate and call it a tax.

Some legal conservatives have argued that Roberts' ruling on the Commerce Clause was a significant long-term victory. And they say that his additional ruling that states could opt out of the law's Medicaid expansion was a huge win for federalism.

But whether you're a liberal relieved by the ruling, an outraged conservative or one of his defenders on the right, there's no denying the importance of Roberts' health care ruling. In that sense, he should be seen as the person of the year.

Philip Klein (pklein@washington examiner.com) is a senior editorial writer for The Washington Examiner. Follow him on Twitter at @philipaklein.