Mitt Romney's biggest liability might just be his own mouth

After watching Wednesday's debate, it's obvious that the time has come to move to the next phase of the debate over Mitt Romney's tax cut. His tax cut plan remains a massive liability, but it's time to dismantle it using political jujitsu by turning the force of Romney's own words and arguments against him. And it can be done with a simple two-part plan.

First, focus primarily on the fact that Romney is proposing to cut taxes by 20 percent on everybody—including the top one percent. When Mitt Romney talks about his tax plan, he calls it an across the board 20 percent tax cut for everybody, including the top one percent. When Democrats and the Obama campaign talk about it, they generally call it a $5 trillion tax cut. Because the total cost of Romney's tax cut adds up to $5 trillion, that's an accurate line of attack, but Mitt Romney never uses the $5 trillion figure. As we saw on Wednesday, that allows him to muddy the waters.

Meanwhile, there's tons of video of Mitt Romney talking about it as a 20 percent tax cut. It's easier to make that attack stick because it's using his own words against him. Plus, it's easier for people to visualize why it's crazy to cut taxes on the top one percent by 20 percent than it is to talk about $5 trillion.

Second, acknowledge that he has offered one scenario in which his numbers add up: the voodoo trickle-down scenario under which cutting taxes on the wealthy magically creates so much economic growth that it doesn't add to the deficit. Every independent analyst who has looked at Mitt Romney's tax plan says that his numbers don't add up—and that to pay for it, he'd have to raises taxes on the middle class or add to the deficit. That's a good and accurate argument, but as we saw on Wednesday, Romney can answer it by simply saying that he would never raise taxes on middle class or add to the deficit. Unfortunately, simply citing independent analysts isn't a slam dunk way of rebutting such an assertion—even though it's right.

A better approach is to use Mitt Romney's own arguments against him. Here's what he said during the debate: "I also lower deductions and credits and exemptions, so that we keep taking in the same money when you also account for growth." On Thursday, his campaign has endorsed an AEI analysis making exactly the same case.

On the one hand, acknowledging that Romney is making this argument concedes that he has in fact outlined one scenario in which he is able to achieve his stated principles without raising taxes on the middle class or raising the deficit. But in exchange for acknowledging that fact, you get to hang the entire Bush economic philosophy around Mitt Romney—in his own words.

Bush's economic theory was that if you cut taxes across the board, the economy would boom, making up any lost revenue. His ideas failed spectacularly, and everybody outside the Republican bubble knows it. And Mitt Romney is now defending his tax plan using the exact same economic philosophy.

In short, Mitt Romney is proposing a 20 percent tax cut on everybody, including the wealthiest Americans. He says he'll pay for that in part by eliminating deductions and in part by economic growth. In other words, he's claiming to have discovered a new kind of math where if you cut taxes, revenue booms. But he's hardly the first to make this claim, and turning that argument around on him is as easy as pointing out how miserably it failed under George W. Bush.

It's not that there's no value in pointing out that Romney's tax cut would cost $5 trillion or that it would end up raising taxes on the middle class. The problem is that leading with those arguments can be tough sell to undecided voters because Mitt Romney has avoided describing his plan in those terms.

But he does describe his plan as a 20 percent across the board cut for everybody, including the top one percent. And he does admit that the only way his plan adds up is by assuming it will create economic growth. Those are pretty damning words, so let's do some jujitsu on his voodoo.