The chart at the top of this post tells you everything you need to know to understand why Axelrod says that—and why he's right. During the last 22 years, Mitt Romney has revealed just one of his tax returns. He's also promised to release the 2011 tax return when he files it, but until he actually files, that's nothing but a promise.
During the Republican primary, Mitt Romney defended stonewalling on the release of tax returns in political terms. He said releasing his returns would give Obama a political boost, and that he didn't want to help Obama. But even if that's true, Romney is no longer running to represent the Republican Party—he's running to be the president of the whole country. He's got a responsibility to disclose the truth, whether it's pretty or not.
The weird thing is that we already know Mitt Romney is massively wealthy yet pays less than 15 percent of his income in taxes. We already know he has offshore bank accounts—and that he failed to disclose one of those accounts in a previous disclosure. We already know he somehow inflated the value of his IRA to over $100 million.
But the fact that Romney won't release any more tax returns is evidence that there's much more that we don't know—and that he doesn't want us to know. And the big question remains: What is Mitt hiding?