Releasing the 2015 tax return could give Mr. Trump an opportunity to counter that story. He could forgo otherwise allowable deductions to make his tax return more politically palatable. He could do so without imperiling his stated rationale for releasing returns from the recent past, because the 2015 return presumably wouldn’t be under Internal Revenue Service audit at the minute he files it.

He would, however, invite lawyers, accountants and reporters across America to dig through whatever he releases, a concern his sons have raised in recent comments defending his decision not to release the returns.

There’s even a precedent for a candidate releasing a return crafted for public consumption.

In 2012—in a decision Mr. Trump has repeatedly criticized for being too close to the election—Mitt Romney and his wife, Ann, released their 2011 tax return when it was finished in September. Mr. Romney, who had promised that he would pay an effective tax rate of at least 13%, chose not to deduct $1.75 million of the $4 million in charitable contributions the couple made so he could hit that number.