I did see a post proposing another explanation of what the Russians have on Trump to make him so eager to please.
The trouble with any sort of blackmail is that it is an attempt to shame the shameless. I see nothing in Trump's emotional makeup that would suggest he considers himself capable of doing wrong.* A person who thinks he can do no wrong can be extremely difficult to blackmail, no matter what he does.
As an alternative, that person suggested that maybe the Russians loaned Trump a great deal of money are are in a position to bankrupt him by calling it in. No moral judgment there, no fear of exposure, strictly business and the fear of losing money. This is pure speculation, of course, but it seems in character.
*Admittedly there is the pussy tape. Even Trump tried to distance himself from that one.