But why would that be relevant to him being beholden to Russian investors? What sort of connection/conclusion would it forseeably allow us to make?

I guess if Russians were giving him very sweet terms on financing, he might be inclined to 'repay' them by loosening some foreign investment policy. Also - the US currently has a gang of Russians under severe financial control, i.e. they are not able to move a dollar out of Russia. If those guys are connected with 'Russian investors' they might try to lobby to get out of 'money jail'.

But why would his tax return shed new light on this, that his previous financial disclosure did not? Are you saying that the tax return would include detail on things like financing rates that were not mentioned in the financial disclosure? I thought it would just tell us what deductions he was taking / loopholes he was exploiting with respect to his taxes.

>gang of Russians under severe financial control

Lol, what does it mean: under control until the guy opens an account under a fake id

Yes, his tax returns may very well indicate who he is doing business with and roughly on what terms.