Hours before Tuesday's night's presidential debate, Mitt Romney is sharpening his criticism of his rival's tax plan.
The former Massachusetts governor says Herman Cain's "9-9-9" tax plan still needs a lot of work. And he says that most middle-income Americans would end up paying more if Cain has his way.
Cain is a former business executive who recently jumped into top-tier status in the Republican presidential primary contest, buoyed in part by his simple tax plan. He's calling for a 9 percent national sales tax and 9 percent tax rates for personal income and corporations.
Romney criticized the plan on a conference call with supporters Tuesday afternoon. He warns that senior citizens and those on fixed incomes in particular could face significantly higher taxes under the 9-9-9 proposal.