What would be the implications on his presidency to date? Fruit from the poison tree, so to speak, not as it relates to evidence in the true legal sense, but as a matter of policy, etc.
Let's discuss.
If this was legitimate, verifiable collusion proving without doubt Donald Trump working directly in concert with the Russian government prior to the election with the express intent to influence the outcome of the election he would get impeached IMHO. There would be bipartisan support from both political parties in both houses of Congress. That's why the Nixon impeachment worked. And that's also why the Clinton impeachment blew up in the Republican's faces and ushered in a very long lived Democratic Congressional majority.
Speaking for myself, I wouldn't make excuses for him and I would want him gone pronto.