Because of the complexity of our tax code, there are many ways Romney’s returns could have turned out. Rather than earning his money from investments, Romney could have sought salaried work and paid a top income-tax rate of 35 percent. Conversely, he could have put his hundreds of millions of dollars into municipal bonds and paid no taxes at all on that income. That Romney chose one option instead of the others tells us nothing at all about the desirability of his own tax plan, about his probity as a businessman and taxpayer, or indeed about any public-policy question of any consequence. Some critics will say that the fact that Romney typically pays less than 15 percent in taxes is an indictment of our current tax code. But you know who wants to change that tax code? Mitt Romney.

Romney could have played it differently. In response to criticism over his 2011 taxes, he might have pointed out that he has consistently and for many years given away both more in absolute dollars and more as a share of his income than either Barack Obama or Joe Biden ever thought about doing — and they are wealthy men, too. He might have pointed out that his tax-reform plan includes reducing the number of exemptions and deductions given to high-income taxpayers such as himself. But he felt boxed in by his 13 percent assurance.