Again, "Collusion" isn't a crime, it's an element of the crime of Conspiracy. According to law, the 2 conspirators don't even have to know of each other's Existence to both work towards the same ends, and benefit from them. We know that Trump knows Putin, and his people work with his people. There's no reasonable doubt, nor deniability here, not after he requested on National Television for the Russians to interfere with the Election. Ignorance of the Means to that end is as immaterial as ignorance of the law itself. Just because they used that to hack Facebook, and Youtube instead of secure Emails does not make it any less a Conspiracy to commit espionage, and election fraud with a foreign power.
We don't need to prove Collusion.