I’m not sure people have thought through all these choices.
I’m surprised that anyone would say a foreign government having blackmail information would be grounds for impeachment. Really? There could be any number of people that foreign governments have compromising info on. For anyone whose done any wild and crazy things in his youth, there’s probably a good likelihood that foreign intelligence services would come across this info. If you make this a standard, then you would probably be impeaching presidents left and right.
Holding a president responsible for the actions of his subordinates also seems like a completely unworkable line. Scandals during presidential administrations are routine. The traditionally accepted approach is that the actual perpetrators get prosecuted, and the agency heads who allowed it to happen sometimes (but not always) resign. Again, if you start impeaching presidents based on the actions of his subordinates, then you’re going to routinely impeach presidents.
The idea that you can impeach Trump for firing Comey, based on the extremely speculative notion that he was doing this to interfere with the Russia investigation, also amounts to lowering the bar on impeachments to an unrealistic level.
Basically the general idea is that impeachment needs to be an extreme measure. If you start impeaching people over things that most presidents are guilty of - or even that most presidents are seen by the mainstream opposition as being guilty of - it would not be helpful for the government or for peaceful democratic discourse.
As for the poll, #4 & #6 would probably be grounds IMO. But I might differentiate between “knew” and “caused”. “Caused” is definitely grounds IMO. “Knew” is more iffy. If there’s some sort of law against it, then that would be grounds too. Even if there’s no law but the collusion was ongoing, then probably that too. If there’s no such law, and the knowledge was about something that had happened in the past but was not expected to continue, then I would think it’s not grounds. (In fact, I myself would probably not report such a thing myself either, if I was in that position. Because that would sink my campaign for no fault of my own, and for no real purpose. After the election would be another story.) If there is a law requiring reporting, then #2 would also be grounds.
All that said, I think it’s extremely unlikely that there was impeachment-level collusion between Trump and the Russians. Partially because I don’t see what the Russians would have needed from Trump or his people, and partially because an enormous amount of investigating to this point has apparently produced nothing consequential.