That was their job. Trump had dealings with Russia while he was running for president. That was not his job. See the difference?
A private citizen can have dealings with whoever they choose. Freedom and all that. The question is what was the CONTENT of the dealings, and who was involved with the dealings.
- IFF the CONTENT involved policy discussions from Mr. Donald Trump Sr. to the Russians should he win the election, that was improper, and depending on the specifics, MAY depress his GOP support to the point where Congress becomes interested in taking impeachment action.
- IF the CONTENT involved policy discussions from the CAMPAIGN with which Mr. Donald Trump Sr. was not privy, then that is improper, but not impeachable.
- IFF the CONTENT did not involve policy discussions, then nothing improper occurred.
I am assuming you understand all that.