Princeton economist, Harvey Rosen who co-authored the study President Obama cited against Romney’s tax plan, says that Obama misrepresented him and his co-author Martin Feldstein. He did so in an email to the Weekly Standard in which he stated:
I can’t tell exactly how the Obama campaign reached that characterization of my work. It might be that they assume that Governor Romney wants to keep the taxes from the Affordable Care Act in place, despite the fact that the Governor has called for its complete repeal. The main conclusion of my study is that under plausible assumptions, a proposal along the lines suggested by Governor Romney can both be revenue neutral and keep the net tax burden on taxpayers with incomes above $200,000 about the same. That is, an increase in the tax burden on lower and middle income individuals is not required in order to make the overall plan revenue neutral.
The Weekly Standard also provided a reference regarding the mathematics of Romney’s proposal.
You can check the math that shows Romney’s plan is mathematically possible here.