Gorbachev most likely was due to his philosophy.

Trump? He only cares about self.

Unless all is for prep for war vs China, really hard to explain. Bannon is firmly on this idea

Or trump really is a pacifist, or isolationist like vance.
but trump is really hard on Iran and don't forget general Miley famous call with Chinese military . Trump doesn't care about peace.

Blackmail by Putin such as sextape or bribery? Also hard to believe, those weapons were always over estimated, they only work on ordinary people, not some one like trump.

Indoctrinated by Russia? Trump is always a celebrity, where would be the time window for that brainwash.

Mystery, big one. Merkel rumored asked him what Putin had on you? Hopefully we can know 1 day