Simon Rosenberg of the New Democrat Network has noticed something interesting. He went through Mitt Romney’s campaign website to see what tax loopholes Romney plans to close. He couldn't find references to a single one—not on the issue page that summarizes his plan for tax reform and not on the more detailed fifteen-page summary available via hyperlink.

The omission tells us a lot. As you probably know by now, Romney has proposed a tax cut that would cost about $5 trillion in lost revenue. Romney says he’ll offset the cut by closing loopholes, in a way that would neither increase the deficit nor raise taxes on the middle class. But he won't specify which loopholes, perhaps because, according to multiple independent analyses, the math couldn't plausibly work as he says it would.

You may have heard that changed last week, because of an interview that Romney gave to a Colorado television station. That's incorrect.

During that interview, according to the Wall Street Journal, Romney suggested he might try imposing a cap on itemized deductions. But that wouldn't change the math: The three promises would remain incompatible with one another. Besides, according to the Journal account (the only one I can find), Romney wouldn't even commit to that idea. He said simply that it was one example of what he might do. That doesn't really tell us anything.

The question isn't what Romney could do. It's what he would do.