In an interview with the man he described as the “master of the budget,” Fox News Sunday host Chris Wallace allowed Paul Ryan to continue touting his tax plan without asking him to identify the deductions and loopholes Mitt Romney would close to make his tax plan revenue-neutral.

Wallace asked Ryan to estimate the cost of Mitt Romney's proposal to lower all individual tax rates by 20 percent. Ryan refused to answer, claiming it would “take me too long to go through all the math.” But despite repeatedly promising to address the issue, Wallace failed to ask Ryan for specifics about which loopholes he would close to offset the revenue reductions from lowering the tax rates.

In February, when Romney proposed his tax plan, he included “limits placed on deductions, exemptions, and credits” on the rich as one of the ways he would ensure that his tax plan would “not expand deficits.” Since then, neither Romney nor Ryan has revealed specific deductions that they would eliminate in order to prevent the loss of revenue from their tax plan, despite repeated opportunities.

Wallace's missed opportunity is significant. In its scoring of the Romney plan, the nonpartisan Tax Policy Center said that Romney's tax plan would reduce revenues by $456 billion, adding, “According to statements by Governor Romney and his advisors, the remainder of the plan will include policies to offset this revenue loss, although there are no details on how that would be achieved.”