Kremlin has long used ‘kompromat’ to manipulate both allies and enemies
It wouldn't be a surprise if Russia had compromising information on Donald Trump. He first went to the Soviet Union in 1987 to talk about building hotels in Moscow and other cities. And he was willing to be exposed.
World leaders have their bodyguards and own intelligence to keep them safe, both of which he lacked.
His bodyguards wouldn't have been able to operate in the country, so he would have had to rely on Russians.