Again, conspiracy aside, what can they possibly have on Trump? He’s simply an amoral self-indulgent person with a fetish for authoritarianism — this gives Russia and Putin enough to manipulate him with.
The idea that he’s some kind of a sleeping agent/is getting blackmailed and, well, genuinely have Russia’s needs ahead of his own is… stupid. Every possible bit of blackmail that you can have on a politician is already public and Trump supporters simply don’t care. You’re talking about an open racist, a guy who committed rape (probably many times), countless frauds, including those that he got convicted for… heck, this is a guy who’ve tried to stage an actual coup.
Just to be clear: did he ever benefitted from Russia, monetarily or politically? Yeah, all the time. They’ve invested a lot in him, he suits their interests. It doesn’t mean that he’s theirs — he sees this as a win-win scenario where he either gets a massive profit from Russia or from Ukraine by blackmailing the latter into this absurd 500b deal.