The president is a subject of the probe, which is the ambiguous position of possibly being a witness or eventually becoming a target.
As for active collaboration? The DAG Rod Rosenstein told Trump these indictments were coming and their nature. And today Trump decides not to push back on Putin/Russia for these actions, but he impugned Robert Mueller with "rigged witch hunt" claims. Again. That is giving aid and comfort to Putin/Russia by papering over, giving them cover for, attacks/crimes on the United States, its people, its institutions, and at least two candidates.
He has been doing a variation on this for two years: maybe they did it, maybe they didn't, Putin denies it so we should believe that because Putin is a good guy and we should just get along, and maybe it was China and maybe it was a 400 pound fat man in a bed.
And what he is doing is two fold: Demanding Americans believe Trump over Mueller, which is hilarious, insane, and ridiculous. But that's just what this presidency has mostly given us in spades. And then demanding that American believe Putin over Mueller and U.S. intelligence agencies!
Trump says he will "ask the question" again to Putin. The false premise is that there is even a question but that too is active collaboration with Russia by accepting that Putin has a more reliable answer to give than Trump's own intelligence service, and his own DOJ, and the special counsel.
Active collaboration is happening in broad daylight.