If I had to put money on this—on which, I can assure my friends at the IRS, I would most certainly pay taxes—the tax-amnesty/legally-dubious-tax-avoidance theory sounds most plausible. What else would make it worthwhile to stonewall? But even this theory has flaws. For example, if Romney applied for amnesty in 2009, that means the account existed for some time before then, and the McCain campaign should have flagged it. (On the other hand, Romney could have told them it was perfectly legitimate, only to get squeamish when UBS settled. Or not disclosed it at all, as Yglesias suggests.) Likewise, wouldn’t the McCain vetters have picked up the aggressive asset-valuations and Cayman Island hijinks that Graetz describes?

Which is why I wouldn’t rule out a fourth theory: garden-variety rich-guy haughtiness. It wouldn’t shock me if Romney believes that, having earned his money legitimately, and having paid all the taxes he was legally required to pay, questions about his tax returns are simply beneath him. Nor would it shock me if his campaign advisers, while clearly aware of the political damage his refusal is inflicting, have learned that you simply can’t budge the boss on matters of personal pride and dignity. And so they’ve given up.

Like the other Romney tax-return theorists, I obviously don’t have a smoking gun. But I’ve spent a decent amount of time chatting with Romney officials these last few months. And on several occasions I got the distinct impression that there were simply places a Romney aide—even very senior and trusted aides—can’t go with the candidate, at least beyond the most gentle prodding. One of those places is credit (the figurative kind, not financial). As several aides told me, Romney insists on being known as the co-writer of all his speeches. Now, that may reflect reality. But, you know, who cares? Why make it a red line? It suggests a certain prickliness. Another of those places is Ann. A campaign official I spoke with shuddered at the idea of offering tactical advice involving the candidate’s wife. General questions of money and wealth—before you even get to taxes—are yet another of these deeply-fraught subjects.

(An aside: I don’t think Mormonism actually falls into this category. While running for U.S. Senate in 1994, Romney was quite open in discussing his faith in an attempt to educate the public. But the campaign felt that this did them no good—the only thing voters took away was that Romney was a Mormon, a religion they were otherwise ignorant of. So Romney and his advisers made a strategic decision to discuss it as little as possible going forward.)