The Helsinki summit and its aftermath has caused me to change my perceptions of the Trump administration, somewhat.
For background, let me recall Watergate. I followed the scandal avidly, being a good liberal Democrat. But given my preference for Murphy's Law as the best first explanation for mishaps in human society, I gave Nixon a lot of slack for a good while. It was conceivable that Henry II (who will rid me of this tiresome priest vis a vis Becket) was a good historical reference. In other words, no top-down plan being executed, but a messy tangled web of interactions.
This general approach was gradually eroded: John Dean's testimony, the tapes, and the revelation of the tape contents. So now I believe, that while there were messy elements, Nixon was the impetus and responsible for the coverup, if not certainly for the initial breakin.
Helsinki caused me to remember this progression and to see the parallels with Trump and Russia. I don't think there's proof of collusion, but I do think Trump set the climate of an unconventional campaign not concerned with past norms. As an underdog the campaign was willing to do anything that offered promise--witness Donald Jr's reaction to the offer of dirt.
Without tapes and/or witnesses flipping, I don't think there's a case for impeachment, not a case strong enough to be prosecuted. The Democrats should only pursue that if it's likely the Senate would convict.