President Barack Obama has claimed that Mitt Romney's tax numbers do not add up, arguing that the Republican presidential candidate's promise to lower tax rates for all families can't be paid for without cutting popular tax deductions for middle class families.

Vice President Joe Biden repeated the claim during last week's vice presidential debate, saying, "The only way you can find $5 trillion in loopholes is cut the mortgage deduction for middle class people."

Mitt Romney has argued lower rates will stimulate the economy, and he is emphatic the middle class won't pay.

"I will not under any circumstances raise taxes on middle-income families," he said during the first presidential debate on Oct. 3.