Trump is a buffoon who doesn't care about how his words or actions affect other people. He has an almost childlike understanding of international relations, and probably knows no more about the world than the median adult American. We know this. Why does he need to be a Kremlin agent, even an unwitting one, to behave as he does? The idea barely makes sense.
I think this hits the nail on the head. There's an old proverb: "Never attribute to malice that which is adequately explained by stupidity." These kind of statements from Trump stem from stupidity, not foreign influence.
(For the record, the stupidity is enough of a reason for me to not vote for him.)
