If there is any, and I mean *any*, evidence that Trumps communications to said senior Russian officials came with a "wink and a nod", or indeed anything more specific, then there is every reason for the FBI to get involved....
And of course, selling a third of our Uranium reserves to Russia or selling dual-use technology to Russia doesn't count. It's not important, and was scrubbed from someone's Wikipedia entry.
Thinking through the outrage over Palmer Luckey (Oculus Rift founder) from his support of Trump, and all the crass, oafish things that have happened during this election, one thing seems clear.
The time to address these issues is after the election.
That's the only time where anyone can legitimately claim that their concern is real, and not partisan sniping.
The ends don't justify the means, and it's not worth tearing down the system "just this once". Getting your candidate elected is not worth sacrificing their legitimacy to do it.
If your candidate was worth his/her salt, then you wouldn't need any of these dirty tricks. Right now, the only limits we should have are legal ones.
I note that while Lyndon Johnson was negotiating the end of the Vietnam War, [candidate for president] Richard Nixon called up [Vietnam revolutionary leader] Pol Pot and said that if he delayed negotiations, Nixon would give him a better deal when elected. Negotiations failed, Nixon was elected and the Vietnam war was extended for 2 more years.
This was an American citizen interfering in the political process of the US, and promising aid to our enemy. It was clearly illegal, and the FBI of the time knew about it.
And did nothing. Illegal, and the FBI did nothing. Ring a bell?
Recently, Hillary literally(*) accused Trump of treason. That seems a bit over the line even for Democrats, and it seems illegal on it's face.
But now is not the time to complain, we've let these people have the run of our media, our internet, and our zeitgeist. Let's let it play out for another 6 weeks, then we can carefully examine these things with the benefit of hindsight.
(*) Using the correct definition of literally