This is the rationale a lot of laypeople give - but we need to remember the IRS isn't a bunch of laypeople. The entire purpose of the IRS is taxes - more-or-less.
I'm very confident that, by now - particularly with all the "Never Trump'ers" that surely populate some of the offices in the IRS - we'd have heard something tangible. I'm confident people at the IRS have looked into Trump and The Trump Organization's taxes quite a bit by now, and the lack of any "leaks" or public releases from the IRS or its employees really speaks to there not being anything there - other than complicated multi-national corporation taxes.
The act of not letting every Tom, Dick and Harry look at his personal tax filings and selectively choose pieces to misrepresent for political purposes isn't indicative of wrong-doing. I'm surprised it ever became a thing for any politician to do.
Not to mention Trump just became president in 2016... they've had his entire life to review his taxes. Wouldn't there be a whiff of something foul, somewhere, if there was something nefarious going on there?
Other than disliking the guy - is there any evidence there's any "criminal activity" here?
This particular president has been audited for something like 12 years consecutively as I recall. If there were something there to find, it likely would have been found by now.
Except for the fact that there was a particular bank lending to him, the only bank in the world that would lend to him, because American banks would not.
And that bank is currently under investigation for money laundering activities for people in a certain other country; and many of those people have cozy relationships with the government of that country. And Trump is particularly cozy as POTUS with the leader of the government of that country.
So - what if the "other" amounts on his tax returns happen to match up in some way with certain amounts on the books with that bank?
I don't know - I'm not an expert in these matters - but something tells me it wouldn't bode well for Trump, and that might be the reason he's so cagey about his tax returns.
After all - if there were nothing there, he shouldn't really care, right? The fact that he isn't "calling their bluff" speaks volumes...
Or the simple fact that almost nobody are tax experts and almost everybody would like to selectively pick pieces and misrepresent them for political purposes.
What would he gain by releasing them? What would anybody gain by releasing theirs?
On a side note, this friend of mine thinks the reason why the President isn't showing his returns isn't because of Russia but because his accountants may have done false filing of some shady business deals and the release of this data will place the President under serious legal troubles.