The other day, Time magazine’s Michael Scherer weighed in with a great post reporting that one of the wealthy individuals who would be impacted by Obama’s push for the “Buffett Rule” is none other than Mitt Romney.

As Scherer noted, much of Romney’s income comes from investments, making him exactly the sort of “millionaire and billionaire” that Obama has been talking about — those who pay a lower tax rate than many middle class taxpayers.

Now it looks like Obama’s outside allies are picking up this line of attack. Earlier today, Priorities USA Action — the group that has vowed to raise huge money for Obama’s reelection — put out a statement responding to an attack ad by the Rove-founded American Crossroads. The news in the statement, which comes from Bill Burton, is the swipe at Romney:

“The billionaires and oil companies funding these ads are desperate to stop President Obama’s plan that would ask them to pay their fair share in taxes to reduce our debt and create jobs. Mitt Romney, Rick Perry, and Karl Rove will spend millions on false television ads because they know that the American public strongly supports the President’s plan that will finally ensure billionaires do not pay a lower tax rate than middle class families. No fair-minded American thinks that someone like Mitt Romney should pay an estimated 14 percent tax rate while hardworking Americans are paying far more.”

This is a sideswipe, but it’s a significant one. Clearly, if Romney becomes the GOP nominee, Obama’s outside allies (if not the Obama campaign itself) will turn Romney himself into the public face of the very sort of tax unfairness Obama is seeking to rectify. This is one of Romney’s unexplored vulnerabilities.

It’s been widely pointed out that Romney would have a tough time making a general election issue out of Obama’s health care plan, since Obama can reply by thanking him for his pioneering approach to health reform in Massachusetts and his role in creating the model for the hated “Obamacare.” But tax fairness may be even more central to the 2012 campaign than health reform. Romney would seem to be a less than ideal messenger to rebut Obama’s call for fairer taxation, since an argument over the topic will serve to highlight that Romney himself is profiting handsomely from the current unfair tax rates that Obama is calling out as stacked against the middle class.