Martin O’Malley, the Democratic governor of Maryland, made a hard-charging case for President Barack Obama and against Republican nominee Mitt Romney.



"And yet Mitt Romney and Paul Ryan now say they want to take America back. And we have to ask: Back to what? Back to the failed policies that drove us into this deep recession? Back to the days of record job losses? Back to the days when insurance companies called being a woman a ‘pre-existing condition,’ " O’Malley said, speaking at the Democratic National Convention in Charlotte, N.C.



"No, thank you. I don't want to go back. Do you? Instead of a balanced, achievable plan to create jobs and reduce the deficit, Mitt Romney says, puts forward a plan that would cut taxes for millionaires while raising them for the middle class."



We should note O’Malley’s remarks were modified from the advance transcript sent to reporters. In the advance version, O’Malley said more simply, "Mitt Romney says he will cut taxes for millionaires and raise them for the middle class."



The idea is clear enough, though: Romney wants to cut taxes for millionaires while raising taxes on the middle class.



So does he?



That’s not how he would explain his own plan. Romney would say he wants lower tax rates for everyone.



But it’s not quite that simple. Let us explain.



Romney’s tax plan



Generally speaking, Romney’s plan would lower tax rates for everyone while getting rid of exemptions, deductions and loopholes. That way, people would pay lower tax rates, but more income would be subject to taxes, so the changes wouldn’t blow a hole in the deficit.



Other ideas from his tax plan: eliminating interest, dividend and capital gains taxes for taxpayers earning less than $200,000; eliminating the estate tax; repealing the Alternative Minimum Tax; and cutting the corporate rate to 25 percent.



Romney has said he wants to keep tax rates low on savings and investment, which tend to benefit the millionaires. But he’s also said that people at the high end "will still pay the same share of the tax burden they’re paying now," which suggests he wants to maintain the current progressive system where people pay more taxes as a percentage of income if they make more.



The biggest sticking point -- especially for fact-checkers and independent analysts trying to analyze Romney’s plan -- is that Romney hasn’t specified what exemptions, deductions and loopholes he wants to get rid of. It’s impossible to tell if Romney’s math adds up.



The Tax Policy Center analysis



One group that’s tried to unpack his plan is the Tax Policy Center, a nonpartisan tax analysis group that has analyzed tax plans put forward by candidates and officials. The group's report, first published on Aug. 1, 2012, analyzed Romney’s plan by choosing common exemptions and deductions to scrub from the tax code.



The Tax Policy Center had to choose on its own what exemptions and deductions to get rid of, but the analysts tried to select the ones that most conformed to the principles Romney has outlined. (The Tax Policy Center refers to them as "tax preferences.")



Still, the math didn’t work. If the tax plan is to generate the same amount of revenue and offer across-the-board tax cuts, some exemptions for the middle class would go away. "As a result, a revenue-neutral reform within these constraints would cut taxes at the high-end while raising them in the middle and perhaps bottom," wrote Donald Marron, the center’s director, in a blog post about the study.



Meanwhile, the across-the-board rate reductions would benefit the wealthy, who overall would see lower tax burdens, according to the center’s analysis.



The Obama campaign has used the study as evidence for its claims that Romney’s plan means tax increases for the middle class. When the campaign puts those claims in the proper context, it’s a reasonable point. Romney’s tax plan is lacking in details, and the Tax Policy Center’s conclusions are compelling evidence. Depending on how the Obama team has phrased it, we’ve rated their claims anywhere from Half True to Mostly True.



In this case, O'Malley goes too far to declare Romney’s plan a tax increase on the middle class.



Marron of the Tax Policy Center says there is insufficient evidence for the harsh Democratic talking points that have evolved since the policy center released its report: "I don’t interpret (the report) as evidence that Gov. Romney wants to increase taxes on the middle class in order to cut taxes for the rich, as an Obama campaign ad claimed. Instead, I view it as showing that his plan can’t accomplish all his stated objectives. One can charitably view his plan as a combination of political signaling and the opening offer in what would, if he gets elected, become a negotiation."



Supporters of Romney’s plan have said it’s not fair for the Tax Policy Center to select which tax preferences to get rid of, and that they’re assuming tax increases that aren’t part of Romney’s plan. We reviewed their study and found that it did make assumptions, but that those assumptions tried to give the Romney campaign the benefit of the doubt.



Our ruling



O’Malley said at the Democratic National Convention, "Mitt Romney . . . puts forward a plan that would cut taxes for millionaires while raising them for the middle class." Actually, Romney’s plan includes across-the-board tax cuts for everyone, including millionaires. It does not specifically include tax increases on the middle class.



But Romney’s tax plan is vague and doesn’t appear to be able to keep all its promises. Romney has said he wants to eliminate deductions while cutting tax rates for everyone; bring in the same amount of revenue for the government; keep a higher burden on the wealthy; and keep low rates on savings and investments. A credible, independent analysis shows these goals are in tension with each other and don’t add up. The Romney campaign has repeatedly declined to offer more specifics.



In the past, the Obama campaign has pointed to this report and framed its claims more carefully, and we’ve given them positive ratings when they’ve done so.



Here, O’Malley is blunter. He says that Romney plan "would cut taxes for millionaires while raising them for the middle class." It might, but that’s not what Romney says his intentions are. Instead, he would like rate cuts for everyone. We rate O’Malley’s claim Half True.