I disagree about the Russia investigation.
In the right wing media, and in some parts of the left wing media, the Russia investigation is about whether the Russians participated in illegally or improperly rigging an election, and therefore showing that Donald Trump is not the legitimate President. In that sense, your description fits.
However, in the halls of Congress, and for the rest of the voters, the Russia investigation is all about what ties the President of the United States has with Vladmir Putin, or other Russian contacts. Russian influence on the election is a small part of that, but no one who can be taken seriously is suggesting that the Russians somehow stole the election. On the other hand, they did seem to want Donald Trump to be President, and a bunch of people close to Trump seem to have a lot of contact with Russians. That is something that makes people very curious.
I don't know if the (former) FBI director had anything to do with that in any meaningful way, such that his departure would be significant to the investigation. However, I know that the real thrust of any Russian connection has nothing to do with rigging an election, but rather on finding out why they were interested in the first place.