Last night, newly ensconced Republican vice presidential nominee Paul Ryan sat down for his first solo interview with Fox News' Brit Hume and let slip an admission about Mitt Romney's budget plan -- an admission that's receiving surprisingly little press attention. Asked by Hume when the Romney plan would balance the budget, Ryan said he didn't know because "we haven't run the numbers on that specific plan."

First, Mitt Romney has been going around telling everyone that, if elected, he intends to balance the federal budget by the end of his second term, or shortly thereafter. Ryan says that they don't know when Romney's plan will balance the budget. If Ryan is right, then what is Romney basing that claim on?