So somebody read Mitt Romney the riot act. The individual-mandate penalty, he affirmed in an interview with CBS yesterday, is indeed a tax. This comes two days after a statement by adviser Eric Fehrnstrom that it isn’t a tax, it’s a penalty. Why the contradiction? Because Fehrnstrom’s comment was a scimitar through the kneecaps of congressional Republicans for reasons that will be explained. But I bet Romney thinks—for reasons that will also be explained—that he can scare Obama and the Democrats with the T-word. And maybe he can. But I think Romney has more to lose from the penalty being called a tax, and the Democrats should call him here, as we say around the poker table, and raise. This is a tax debate with Republicans that Democrats can actually win—if they’re not afraid to have it.

The instant after the court decision a week ago, you’ll recall, congressional Republicans took the gist of the court’s finding—the mandate stands as a tax, not a penalty—and launched into a campaign calling the ACA the biggest tax hike in all of American or even human history and saying that Obama broke his promise not to tax middle-income Americans. Politifact rated the first claim pants-on-fire false. As a percentage of GDP, in fact, it’s only the 10th largest tax increase in America since 1950. The second claim isn’t exactly an all-out lie like the first one, but it’s a grotesque exaggeration, since this penalty-tax would not be paid by everyone, but only by those who refuse to buy insurance, an explicitly self-selecting maybe 2 percent of all people.

Of course, the fact that something is a lie has never stopped the GOP, so that was the strategy coming out of the decision: Obama the taxer. That was the line on last weekend’s shows. But there was a problem. If Obama’s mandate penalty is a tax, then so is Mitt Romney’s—present tense, because people are still paying it—in Massachusetts. Hmmm.

Thus, Fehrnstrom on Monday on MSNBC: “The governor has consistently described the mandate as a penalty.” He had to—otherwise, Romney is a tax-raiser. But in saying that, Fehrnstorm destroyed the whole congressional Republican line of attack against Obama. How credibly can Eric Cantor and the rest of them stand up and call the mandate a tax increase when their own party’s nominee (through a top aide pretty obviously dispatched to say precisely what he said) says the opposite?

Well, this thought apparently occurred to Cantor over the last few days, as well as (probably) Karl Rove and many other Republicans. I would imagine they let Romney know their views on the matter, and told him that he—not Fehrnstrom or spokeswoman Andrea Saul, but he himself—had to walk back Fehrnstrom’s remark. “But I can’t say that,” he must have told ... someone. “Because I did the same thing in Massachusetts, so if this is a tax, then I’m a tax-raiser like Obama!” “That may be,” said someone. “But we’ve got 435 House candidates and 33 Senate candidates who need to be able to call this a tax.” And my someone may well have added something like: “Plus, governor, you’ve got some very wealthy super-PAC donors who think it’s a tax. Given all that, what’s your view?” So, through clenched teeth, he spit it out.

The net effect is that Romney is, however against his own will it might be, prepared to be smeared as a tax-raiser. But he’s making a calculation: He is gambling that the Democrats won’t want to call it a tax, because Democrats are terrified of the word. And based on what we’ve seen, his gamble is correct. The day before Fehrnstrom was calling it a penalty, Nancy Pelosi was agreeing with him. David Axelrod also says penalty. I haven’t heard Barack Obama himself speak to this exact point yet, but we can reckon he’ll say the same, and for the same reasons as Romney: If it’s a tax, then he’s a tax-raiser.

That’s what Romney is going to say. Then the ball will be in Obama’s court. The indications are that he’ll just say he thinks it’s a penalty. But that won’t fly, I don’t think. The Supreme Court said it’s tax. His administration’s own brief to the court said it’s a tax. It’s a tax. (Actually, in common-sense terms, I don’t think it’s a tax at all, but legally it is, and the court said so, and that’s what matters.) So instead of saying it’s a penalty, Obama should say, “Well, OK, if it’s a tax, then it’s a tax that you imposed, governor. So you raised taxes too.”

That may hurt Obama, but I think it clearly hurts Romney more. Romney comes from the party where raising one cent of taxes is verboten. He has said a thousand times on tape that he never has and never would raise taxes. Now he’s admitting he has—to a base electorate that hates taxes more than anything in the world. If the Democrats stick with the “penalty” line, Romney never has to explain that. And that is exactly what he’s banking on.

It’s a tough needle for the Democrats to thread, and I don’t know exactly how they do it. But I know this much. Romney agreed to call the penalty a tax because he’s hoping the Democrats won’t call him on it. That alone means they should. After all, it’s less shocking to people that a Democrat raised a little tax than that a Republican did—and it’s far more demoralizing to the Republican’s base and his down-ticket surrogates. The Democrats, if they play this smartly, can drive a huge wedge between Romney and congressional Republicans. In a dream scenario, they might even force Romney to defend the mandate—that is to say, they could get Romney so tied up in knots that he ends up defending Obamacare!

Did Rick Santorum have a point when he said that Romney is “the worst possible person in this field to put up [as nominee] on this most fundamental issue of this campaign?” Uh, yes.