It is unproven that Trump is literally a Russian spy although that was not at the time even asserted. The entire issue was that Trump's campaign met with literal Russian spies at a time when Trump was in fact in the building although not verifiably at said meeting. The Russians received data useful insofar as targeting the American people with disinfo.

Subsequently Trump called for the Russians to attack the Democrats. They did. They also appear to have targeted the American people with disinfo which could have been aided by the data supplied to them. Ultimately Trump's position towards Russia has evolved into an uncharacteristically and uniquely favorable position for an American president.

If he isn't an actual asset he certainly at least collaborated and communicated with them as a fellow traveler with similar aims at odds with the actual geopolitical aims of America as a nation.