A good step towards exonerating him would be releasing his taxes, honestly. I know he has said that they're under audit, but I'm sure he can have it fast tracked or something, if that's legal.
He did say the reason they couldn't be released was because of an audit. As pretty much everyone, iirc up to and including the IRS, said, that was complete and
utter bullshit. There were actually other people that were under audit that released theirs during the period in question, if I'm not misremembering. The audit claim was one of the most blatant lies of the campaign, amazingly enough considering how many other ones there were.
As someone with some accountancy/auditing training: There's pretty much zero negative legal consequence to releasing your taxes
during an audit, save in the numbers revealing criminal activity or whatnot and getting your ass busted, nevermind at any other time. Vanishingly little situations where that's a legal problem, none of which we had any indication was happening, and frankly most of them involve issues related to financial ties to criminal or otherwise legally infringing organizations when being made public might alert them (and still usually aren't
illegal, far as I'm aware, save in that it might count as investigation obstruction
and I don't think anyone has actually had charges of that nature stick in US history, so...). There ain't much you can get involved in where releasing your tax returns is going to cause problems for you or anyone else, save to whatever extent bullshit is revealed by them, and most of 'em are ones that say some pretty serious things about the dealings of the individuals involved.
Really, about the only reason to not release the information is a desire for privacy, stuff along those lines. Which while something an american citizen
is largely entitled to, at least in relation to other citizens, is sketchy as hell from the perspective of someone running for high office. Especially considering the previous tradition of doing so. Not that we didn't know all that a while back, but maybe someone could have stood a refresher on the subject.