“President Obama continues to distort Mitt Romney’s economic plan. The latest? Not telling the truth about Mitt Romney’s tax plan.”

– A new Mitt Romney campaign ad

“So lowering the rates, as Mitt Romney has said he would do, to 20 percent: $2.7 trillion over 10 years. Eliminating the AMT (alternative minium tax): $700 billion. Repealing high-income payroll tax: $300 billion. Ending estate tax: $150 billion. Lowering the corporate rate from 35 to 25 (percent): $1.1 trillion. That adds up to $4.8 trillion. If you factor in interest for additional borrowing, you get to $5 trillion.”

– Jennifer Psaki, the Obama campaign’s traveling press secretary, on Sunday

Five trillion! It’s such a big figure.

President Barack Obama says Mitt Romney wants to cut taxes by $5 trillion over 10 years; Mitt Romney adamantly denies it. He has a new ad slamming Obama for this claim – while repeating a charge that Obama has a secret plan to raise taxes.

So the question arises: Is the Obama claim accurate?

Obama spokeswoman Psaki laid out the math to reporters Sunday. There’s just one problem: Romney also has said he will make his plan “revenue-neutral” by eliminating tax loopholes and deductions, much as Ronald Reagan did when he passed his 1986 tax reform.

And there’s another problem: Romney has not provided many details about which deductions he would eliminate. He has suggested that the home mortgage deduction, charitable contributions and employer-paid health insurance might be protected; he has also indicated he is thinking of some sort of cap on deductions.

Moreover, the nonpartisan Tax Policy Center has analyzed the specifics of Romney’s plan thus far released and concluded that the numbers aren’t there to make it revenue-neutral. In last week’s debate, Romney countered that “six other studies” have found that not to be the case, but those studies actually do not provide much evidence that the proposal – as sketchy as it is – would be revenue-neutral without making unrealistic assumptions.

Given the uncertainty, the Obama campaign has assumed the worst about Romney’s plan – that it would mean higher taxes for middle-class Americans – even though, as Romney has stated, there is no chance he would try to implement such a plan as president. Moreover, the director of the Tax Policy Center has taken issue with Obama campaign ads making such claims, saying the organization’s study merely proves that Romney’s numbers don’t add up.

Romney appears to want to have his cake and eat it, too – getting credit for cutting rates without detailing exactly what the impact would be for taxpayers once revenue is recaptured by curtailing tax deductions.

By itself, Team Obama’s $5 trillion claim is an overstatement. Clearly the campaign recognizes that Romney hopes to cut the cost of the tax cut, because it also slams him for the supposed impact of eliminating deductions. So the figure reflects just half of the story about the plan – just as Republicans complain about the cost of “Obamacare” without acknowledging the tax hikes used to make it revenue-neutral in the first 10 years.

Still, Romney has left himself open to criticism because he has not specified how he would fill the $5 trillion hole created by his tax plans. If he released fuller details, he would be on firmer ground to complain about Obama’s assumptions.