Republican underdog Tim Pawlenty declared war on Mitt Romney yesterday by sinking his teeth into the Mittster’s Achilles heel.T-Paw faces an uphill climb to the Republican presidential nomination, and he won’t get much traction, in the polls or the money competition, unless he can convince the Republican base that he’s the best alternative to Romney. Hence his appearance on Fox News Sunday, where he rhetorically gnawed at the frontrunner’s biggest vulnerability.Grassroots Republican hate the Massachusetts health reform law that Gov. Romney brokered in 2006 – especially the individual mandate, the requirement that all state citizens buy health insurance – and Pawlenty sought to fuel their ire yesterday by deriding the law with a new pejorative nickname:”President Obama designed ObamaCare after RomneyCare, basically made it ObamneyCare.”Pawlenty told Fox News that the two health reform laws have “essentially the same features. The president…patterned ObamaCare after what happened in Massachusetts. What I don’t understand is that they both continue to defend it….I strongly oppose the individual mandate at any level. I’m one of the parties in the lawsuit in Florida, trying to get it declared unconstitutional. I think it’s a dramatic overreach by government, forcing a consumer to buy a good or service….I was asked to consider a mandate on several occasions as (Minnesota) governor, and I rejected it every time.”Assailing the mandate is not exactly new – but “ObamneyCare?” That kind of coinage was precisely the inverse of Minnesota Nice. If even T-Paw is willing to bare his teeth, surely it means we are entering a feistier phase of the Republican race.Tonight, for the first time, Romney is slated to debate his rivals on national television (he currently tops the GOP field with 24 percent of Republican voters nationwide, according to Gallup), and the odds are high that he’ll spend much of his stint on CNN fending off charges and insinuations that he’s a slick, squishy, flip-flopping moderate – and, worst of all, that he’s merely Obama Lite. And, as long anticipated, his health reform law will be invoked as Exhibit A. After all, Romney was the first (and remains the only) governor to enact a health insurance mandate. Conservatives loathe the idea of a mandate, because it messes with their freedom to go without coverage and thus freeload on the health care system and other taxpayers in the event that they do get sick. These defenders of liberty are expected to vote heavily in the early Republican primaries; hence T-Paw’s Sunday ambush on “ObamneyCare,” setting the stage for tonight’s debate.Romney will likely try to deflect the attacks by focusing his ire on President Obama’s economic record – suggesting, in essence, that Republicans should refrain from fighting each other and instead unite against the common enemy. But it’s too early in the election cycle for a lofty message. It doesn’t matter that Romney excels in the polls as Obama’s most competitive opponent, because the party base isn’t thinking yet about the general election. That phase is a long way off.Right now, we’re only on the cusp of the intramurals, the junkyard dog phase. Nobody on that stage tonight can rise very far without first taking chunks out of Romney. And the Romney health coverage requirement is ideal for the task. Granted, the whole idea of a mandate was originally hatched by a conservative think tank back in the early ’90s – as a way to get people to take responsibility for themselves – but most candidates and viewers have no historical memory, and, besides, Romney has extolled the mandate concept as recently as 2007. To wit: “I think it’s a good model for other states….Those (states) who follow the path that we pursued will find it’s the best path, and we’ll end up with a nation that’s taken a mandate approach.”Worse yet for Romney, here’s more debate grist for T-Paw:As Pawlenty mentioned yesterday, he’s a plaintiff in one of the federal lawsuits that seeks to overturn the Obama coverage mandate as unconstitutional. Care to guess the identify of one of the parties that has filed an amicus brief in defense of the Obama health mandate? Answer: The state of Massachusetts – which, in its defense of the Obama mandate, invokes the wisdom of the Romney mandate. And it quotes approvingly from Romney himself.In a letter dated July 20, 2005, here’s what Romney told the Massachusetts legislature: “…it is fair to ask all residents to purchase health insurance or have the means to pay for their own care. This personal responsibility principle means that individuals should not expect society to pay for their medical costs if they forgo affordable health insurance options.”All told, Massachusetts’ lawyers declared in their April 11 amicus brief: “Governor Romney and the Massachusetts legislature, like Congress, determined that an individual health insurance mandate, as part of a comprehensive reform package, would serve to increase access to healthcare while greatly decreasing the detrimental cost-shifting caused by people who chose to forgo insurance and shift the cost of their current and future healthcare to others.”I doubt that any of Romney’s rivals will quote from the brief tonight; those wordy passages are ill-suited for a TV audience’s ADD. But no matter. T-Paw’s “ObamneyCare” coinage might be enough to slow the frontrunner’s stride, at least for a news cycle or two. And after all, what other choice does Pawlenty have? When you’re scoring lower in the polls than the guy who made his pile by making pizza, you’d better start snarling.