Biden laughs off Ryan tax talk: 'Not mathematically possible'

Vice President Joe Biden hammered Rep. Paul Ryan over the Republican's tax plan during Thursday's vice presidential debate, alternately dismissing the plan wholesale with a smile, and then obliterating the details as a mathematical impossibility.

Biden charged that Romney and Ryan, by insisting on a full extension of the Bush tax cuts, were, "holding hostage the middle class tax cut to the super wealthy."

"This is unconscionable," he said. "The last people who need help are the 120,000 [highest income] families for another 500 billion tax cut."

Ryan retorted that he and Romney would close enough loopholes in the tax code to pay for a huge tax cut across the board. Doing that, he claimed, would broaden the tax base overall and offset the revenue that would otherwise be otherwise lost by reducing rates—a claim disputed by most economic analysis of that plan. Further, Ryan charged that while he and Romney would reduce tax rates on all Americans, his rivals' policy would mean higher taxes for the middle class.

"There aren't enough rich people and small businesses to tax to pay for their spending," he said. Then, turning to the camera he added: "Watch out, middle class. The tax bill's coming for you."

Throughout the tax debate, Biden, and even moderator Martha Raddatz, pressed Ryan to offer specifics on his tax plan, something he repeatedly avoided doing. At one point, after Ryan offered another in a string of vague responses, Raddatz interrupted him, saying simply, "no specifics again?"

When granted a chance to rebut Ryan's claims, Biden appeared even more animated than at almost any other point in the debate. He suggested that Romney would not really close the tax loopholes he's promised to close because he used loopholes to drop his effective tax rate to an unusually low fourteen percent. And when Ryan chimed in to try and defend his plan, Biden cut him off.

"Not mathematically possible," he intoned.

Ryan pressed on, invoking John F. Kennedy's tax policy, only to once again be silenced by Biden.

"Oh, now you're Jack Kennedy?" he asked, chuckling and flashing a smile.

Watch part of the tax debate below: