During Thursday evening's debate, vice presidential candidate Rep. Paul Ryan (R-Wis.) did not offer new details on the Romney campaign's promise to slash taxes without losing the government a ton of revenue.
The centrist Tax Policy Center has analyzed the plan and concluded that it would create wide budget deficits unless the Romney administration hiked taxes on the middle class. The Romney campaign has insisted that it would not.
"What we are saying is lower tax rates across the board and close loopholes, primarily to the higher-income people," Ryan said on Thursday. "We have three bottom lines: Don't raise the deficit, don't raise taxes on the middle class and don't lower the share of income that is borne by the high-income earners."
Among other things, the plan would cut all individual income tax rates by 20 percent.
"Let's talk about this 20 percent," debate moderator Martha Raddatz said to Ryan. "You have refused yet again to offer specifics on how you pay for that 20 percent across-the-board tax cut. Do you actually have the specifics, or are you still working on it, and that's why you won't tell voters?"
Ryan said that his plan would deny loopholes and deductions for higher-income earners, but he didn't specify whether the plan might target deductions for mortgage interest or charitable giving, for instance. "We want to work with Congress on how best to achieve this," he said.
Raddatz asked, "You guarantee this math will add up?"
"Six studies have verified that this adds up," Ryan said, repeating a claim Republican presidential nominee Mitt Romney made in last week's debate against President Obama.
The claim is debatable. As HuffPost has reported, three of the studies are blog posts or op-eds, and one was paid for by Romney for President Inc. (And the author of two of the pieces highlighted by the Romney campaign suggested the tax plan only works by eliminating tax preferences for people making more than $100,000.) But the supporting research for Romney's plan argues that the Tax Policy Center ignores the way the Romney tax reform would boost the economy, resulting in additional revenue.