Remember in March, when former senator Rick Santorum got a lot of grief for saying that Mitt Romney was the "worst Republican" in the country to challenge President Barack Obama on health care reform? Well, turns out he was right.

That was evident Wednesday when former governor Romney decided he couldn't leave well enough alone and, in a CBS television interview, declared Mr. Obama's individual health care insurance mandate was a tax. That directly contradicted what his campaign had been saying on the subject for two days and left the Republican in the uncomfortable position of having to explain why his own version of health care reform in Massachusetts, which also carried a mandate and a similar penalty, was somehow not a tax.

The candidate's logic is, to put it kindly, nuanced. It's a tax because the Supreme Court says it is, Mr. Romney says. And that's essentially true; it is the federal government's taxing authority that preserves the individual mandate under the court's recent ruling.

So why isn't the Massachusetts provision a tax, too? Because the court doesn't speak to state programs, state constitutions or state authority. "Massachusetts' mandate was a mandate, was a penalty, was described that way by the legislature and by me, and so it stays as it was," he said.

In other words, it may have the exact same effect, but it can't be called the same thing — and therefore the two things aren't equivalent. Doesn't that make perfect sense?

That Mr. Romney could spout such nonsense with a straight face is really quite remarkable. It would have been far easier for him to have simply begged off the question of labels and restated his opposition to "Obamacare" and his desire to see it repealed if he wins in November. After all, he said shortly after the ruling that he sides with the court's dissent (a group, by the way, that didn't buy into the majority's opinion on the tax argument).

But no, he had to echo the "nyeah, nyeah" line from the conservative wing of the GOP that Mr. Obama has raised taxes on the middle class after promising that he wouldn't. And here's the sad thing: Even the conservatives aren't real excited about his flip-flop on this issue.

In a lead editorial, "Romney's Tax Confusion," The Wall Street Journal said the belated change of heart has caused the campaign to appear "confused in addition to being politically dumb." The Journal further complains that the GOP candidate appears to be losing ground and isn't making a coherent case against the Democratic incumbent.

And that's before Mr. Romney has even had a chance to formally accept his party's nomination at the Republican National Convention. Ouch.

In real life — you know, the place where most of us live — whether the penalty paid by those with sufficient income to afford to buy health insurance but choose not to is a tax or a penalty is about as important as how many IRS agents can dance on the head of the pin. The law didn't change in substance from when it was approved by Congress two years ago. The court (and chiefly its chief justice) just ruled under what legal authority it operates.

Only in Right-Wing-World, where everything called a tax is evil — but apparently "penalties" are perfectly fine — is this distinction important. But Mr. Romney is no longer running in a primary. He should be in the business of trying to demonstrate to swing-state independents and Democrats that he's capable of leading from the center.

But alas, he has fallen into the trap that he always seems to fall in — the desire to cater to his party's most extreme voices. Once it became clear that conservatives wanted to play up the Affordable Care Act as a tax measure, he had to join the crowd, even if it meant contradicting a top aide and others in the campaign. The fact that Massachusetts' "Romneycare" also made him vulnerable on the tax issue was apparently unimportant, too.

We don't know that health care reform will be a central issue of the 2012 election, but even if it is, chances are good that the penalty/tax debate won't be the pivot point. Instead, the episode will likely be remembered as an obvious example of Mr. Romney's tendency to recalibrate his views for political convenience — a behavior that is threatening to define his candidacy.