My read of the situation is that he was (and continues to be) a "useful idiot."

The Russians would not be so foolish as to make him an actual agent (regardless of what Trump's aims or goals are). It is much easier and better for them to collude with Trump along lines of common interest (as the various parties see it) in an unofficial capacity.

Trump is basically too untrustworthy, loudmouthed, and stupid to be recruited as an agent... and he is basically so oblivious to anything but his own immediate needs and interests that he will willingly do what you want him to do without you telling him anything.

he is that glorious and much desired combination of ego, selfishness, influence, and lack of critical intelligence that is in high demand for people looking to do underhanded things and keep their own hands clean.