During the Republican debate on Monday, Mitt Romney suggested that he might release his 2011 tax return, but only in April. On Tuesday, he told reporters that his effective tax rate was “probably closer to the 15 percent rate than anything.”

Mr. Romney is clearly hoping that by drawing this process out for another three months, and copping to the low rate early on, he will deflect at least some of the shock about the size of his personal wealth and what a great deal you get from the government if, like Mr. Romney, you make most of your money from investing.

Let’s be clear: despite Mr. Romney’s claim that “people will want to see the most recent year,” his 2011 taxes would not be enough. Voters have a right to know how...