We already know that elements of the Trump campaign both discussed illegally obtained info with the Russians, coordinated secret meetings in order to discuss it, and then lied about it.
We know that Trump openly encouraged foreign entities to “find” dirt on his political opponents.
We also know that Trump’s campaign/administration repeatedly responded to these Russian efforts by seeking to ease sanctions and political pressure on them.
It’s a textbook example of collusion. The fact that some will not accept anything less that Trump caught on tape saying “I am colluding with Russia to interfere in the election.” doesn’t mean that it wasn’t taking place or that there is not clear evidence of it.