I read the law in question a while ago. I think I may have encountered it during a completely unrelated tax research project instead of looking for it specifically, but that’s not too relevant. It was quite clear that the two Chairmen of the committees in each chamber of Congress have the right to request absolutely anyone’s tax return. However, after doing so they must not disclose any information in it to the general public.
However , I think people in general are overly optimistic about the kinds of things that are found on an actual tax return. You don’t report to the IRS every single detail about what’s on your returns - you provide summaries and occasionally there are times you need to file required statements when the amount of space on the forms is too small to fit what’s required by the form, but in general, the returns are only the very broadest of strokes.
There is a little bit of detail you will get, and that’s who their employers are and what pass-through entities they are receiving income from. That all shows up on the return, associated with a federal taxpayer number (TIN/EIN, like an SSN), but seeing them there isn’t going to tell you the nature of their business (besides what you can tell from how the K-1 income is divvied up among the various types of income). Of course, if they can subsequently request that business’s return they can get more information about them, such as the other partners, but it still won’t tell you anything much about the details of the business. If they have real estate rentals they’ll tell you what addresses they have, but for other kinds of business transactions, there is no such requirement to report the sources of income and the identities of those to whom expenses were paid. A total interest expense will be reported, but no details of who the interest is paid to. The balance sheet will list how much debt they have, but not to whom it is owed. Although you are supposed to report debt from owners of the business separately, that doesn’t tell you which owner holds that debt.
I’m not sure what people expect to find on Trump’s tax returns other than that he simply isn’t nearly as wealthy as he leads people to believe. That’s what Trump is really hiding, because if he has extra-legal business associations, it would be relatively simple to just not report them on his tax return, or to report what their legal facade was (ie, what was reported to the IRS). Without an audit of the return, you won’t have any idea whether any of the information is actually true with the exception of those few things reported to the IRS like W-2s and K-1s, and even for those, the documents may be based on false information and entirely made up and as long as it’s reported consistently the IRS won’t notice unless they audit everyone involved.
Similarly, you won’t get any information on which charities were donated to. You might type all the information into Turbo Tax and it might generate a detail report that might be included with your return, but that doesn’t mean that in general people are required to report each and every donation. The vast majority of my firm’s clients provide us a list of contributions already added up, we go over the list to ensure they are all legitimate charities because some people like to include political donations on the list, and if everything’s good, we just type the bottom line number into the software. That’s all the IRS sees.
And it’s like that for pretty much every other line as well. “Other expenses” on business returns will be broken out into types, but every individual expense won’t be listed. When people hear about how long some firm’s tax returns are, and there are some doozies in our office, it’s because they have a huge number of different K-1s each with several pages of detail, most of which is blank, or it’s because they have a huge number of properties and can only put 3 on each page plus they may need extra space to itemize all the “other expenses” by type, or it’s because they have a large number of transactions that require reporting because they are a day-trader, or any number of other reasons, but these don’t tell you what entities the businesses were giving money to, only the sources of their income, and then only vaguely.