It’s disclosure all the way down.

If you’ve got the second-worst tax return imaginable, and everyone who is cleaner than you discloses, the public will infer that you’ve either got the worst or the second-worst possible return. Far better to clear up the confusion that you don’t have the most dishonorable tax return that’s possible, and so you also choose to release your tax returns.

Follow this logic, and you’re left to infer that the only person who won’t voluntarily release their tax returns must have the most to hide. It doesn’t just say that Mr. Trump has more to hide than Mrs. Clinton; it says that he has more to hide than any other candidate you could imagine.

Think about it. The problem for Mr. Trump is that the voters don’t know if he’s Honest Donald or some other Donald. But Mr. Trump knows. If he’s Honest Donald, he’ll release his tax returns to make sure that voters know that he’s neither dodgy nor deplorable. And if he’s dodgy, he will release his returns so that we know he’s not deplorable. Only Deplorable Donald — the worst possible Trump — has no incentive to disclose.

By this logic, a candidate would hide tax returns only if they paint a terrible picture about finances and integrity. (If there were the risk that Mr. Trump’s returns would reveal commercially valuable information, that would be a reason that he could be not-seedy yet still want to keep his returns private. He has yet to make this argument, though.)

You actually use this logic every day to make sure you don’t get ripped off. If I were offering to sell you a used car, and refused to let you take it for a test drive, what would you infer? It must be a dud, unable to even start. After all, even if it ran poorly, you would let me drive it, at least to reassure me that it actually does run.

Likewise, you wouldn’t buy stock in a company that refused to show you their books.

This same idea is why you demand the right to inspect a good before you buy it, or if it’s in a box, you demand the right to return it if it turns out to be a dud. You can’t return presidents, which is why voters have traditionally demanded the right to inspect them first.

There’s something distinct about information: Refusing to share it doesn’t keep voters in the dark. If they think about why, the choice not to reveal it is very revealing.