Congresswoman Gabrielle Giffords starts out Monday with another new ad hammering Republican challenger Jesse Kelly. This time, Team Giffords is focusing on Kelly's statement that he'd support a new national sales tax over the current income-tax system.

As we've noted before, Kelly has said he'd support the so-called Fair Tax, but he'd rather do a 10 percent flat income tax because "if 10 percent is good enough for Jesus Christ, it's good enough for the federal government."

The larger problem with the national sales tax is that it would have to be much higher than 23 percent to bring in as much money as the federal income tax. There are much bigger economic problems that come from it, but rather than lay them out here, I'll just suggest you check in with Bruce Bartlett, a conservative economist from the Reagan administration who lays out why he thinks it's a "totally crackpot idea" here.