Should Russian interference have been investigated? Why in the the world not?

Worries about the origin of the investigation seem to imply that somehow we shouldn't have investigated the Russian interference in our election and whether anyone whose candidate benefited from the interference had conspired with them. There was interference by the Russians, it was designed to help Trump, it did help Trump, Trump kept denying that it was happening and welcomed, and welcomed, and welcomed the fruits of that illegal interference.

 It's not an awful thing for there to be a "cloud" over a President's administration, it's called oversight. What Trump has endured is nothing compared to what Nixon had to deal with, or Bill Clinton, who faced an investigation that started with looking into land deals in Arkansas and ended up, well, you know where it ended up.

 I think the most important questions arising from Mueller have to do with the interference itself, and what we need to do about it. Republicans are implying by their actions that the interference was not disturbing, and even the continuation of that interference is not disturbing. (One has to wonder what they would say if the Russians helped put Hillary in, instead). I have seen people say that it's not such a bad thing so long as it digs up dirt on Hillary and the Democrats. That seems to be the view of Trump himself, and seems to be widespread in the Republican party, although they don't normally put it so bluntly. (Maybe it would be a good idea to force them to put it so bluntly). Or does this kind of interference endanger our very system of government? 

They hacked into voter rolls in all 50 states, for crying out loud. What if, next time they did it, they "unregistered" a bunch of people so they couldn't vote? In my view, the real issue isn't collusion (whatever that means), or even obstruction. It is what I call dereliction.

 If Bush, after 9/11, and resisted clear evidence that it was al-Qaeda that attacked us, and refused to do anything to keep it from ever happening again, would that not be upsetting if not impeachable (especially if we couldn't figure out whether Bush was somehow under the sway of bin Laden for business reasons), even if Bush is this behavior broke no criminal laws? OK, nobody died in the cyberattack, just as nobody drowned in Watergate, but do we care about the independence of our electoral system?

 In my opinion, the Democrats, and we as citizens, do best if we keep the cart and the horse straight. They have to start with Russian interference and the complete failure of the Trump campaign and administration to deter it or prevent it in any way. These are undeniable facts. After that, we can raise the question of conspiracy or obstruction.