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Nobel Prize-winning New York Times columnist Paul Krugman said that GOP vice presidential nominee Paul Ryan was "never a man of substance" during our "This Week" roundtable discussion about the Romney-Ryan tax plan that I questioned Ryan about earlier on the program. You can read the full exchange below.

BOOKER: I want to attack this idea, the certainty for small businesses. This is a president who has cut taxes on small businesses 18 different times. He's done enough to target incentives to small businesses, everything, to hire our men and women coming home in addition to the fact to giving them breaks for investment.

So I disagree with that on small business. But I think it's more important, and I really want to call the question that Paul Ryan left wide open, is, how can you call for $5 trillion worth of tax cuts, give us no specifics?

This is Paul Ryan who used to be a man of substance, who put up plans, I may disagree with some of them, but with great levels of specificity. Now they've said they're going to cut $5 trillion in taxes, increase spending in the military, and somehow not dig us into a deeper deficit budget… deficit.

(CROSSTALK)

ROBERTS: This is Bill Clinton and arithmetic. That was a good one.

KRUGMAN: I'm going to disagree, respectfully, he was never a man of substance. This is who he always was. That was always an illusion.

Watch the entire roundtable below:

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