@Jeruba It’s been an ongoing question since 2016. I don’t think I’m in a position to know all of it, but the parts I can see include:
* Russia caused Trump to barely win both elections and not only does Trump know this and so value to massive impact of Russia’s many opinion-shaping intelligence operations, and so want to keep that benefit, he also knows it could be turned against him, AND that Putin could explain it publicly, which would likely undo Trump’s political position in the US.
* Russia probably has other major kompromat/blackmail material on Trump. (Some people tend to dismiss that because of how shameless Trump has been about his sexual assault and infidelity, and his supporters haven’t seemed to care, but I think if it extended to graphic undeniable evidence of pedophilia, sexual violence, homosexuality, murder, etc., that might matter.)
* Putin also seems like the sort of person who has skills Trump wishes he had himself, including skills well suited to playing Trump like a fiddle
* Putin isn’t just head of state, he’s also former KGB, and is also essentially the head of the Russian mafia.
* And, both Russian covert ops and Russian mafia assassinate people, and Trump has talked with them many times over the years, and is a self-serving coward, so I would expect Trump to be afraid of them and want to stay on their good side for that reason.
* Russia is a potential safe harbor for if/when Trump finally finds himself about to be thrown in prison.
* Trump had at least $100 million in declared income from Russians in the period 2008 to 2013. I expect there is even more financial/business assistance from the Russian mafia, and/or other transactions that the Russians have intelligence about that they could reveal that helps Trump want to do what they want.