Actually nat the FBI wasn't investigating the Trump campaign but was looking into foreign governments interfering in US Elections. This is a crime.
When investigating it they kept on ending up with someone from the Trump campaign, talking to them. The FBI thought initially that the Russians were just using the Trump Campaign.
This is what everyone started investigating... Actually no one has said anything about Trump personally involved at first and Mueller has been tight lipped about anything since.
It has been Trump's behaviour afterwards that makes him look guilty, innocent people don't run a propaganda war against the DOJ..
America was attacked, If the President is saying that OK and attacks the investigators, why should any country not be attacking the US in the next election?
There is no repercussions for there actions.
Mueller's problem is his whole investigation had nothing to investigate, from the beginning. Never was any crime committed. Still haven't found one, and investigations are supposed to investigate crimes, not conduct investigations in search of one, or attempt to bend or shape the law to make a prosecution.
Should be interesting to see what happens when the evidences of Clinton crime start being checked out. Plenty to investigate.