Investigation != government sanction. Police action or congressional action to investigate does not require evidence of wrong doing. Are you suggesting every single person brought before the judiciary committee is there because of evidence of wrong doing?
Just like if someone makes a legal purchase for bomb making supplies they can be investigated even if there is no proof they have done anything wrong. The facts warrant review.
1. The guy is very partisan.
2. Due to his behavior (the texts) he was removed from an investigation
3. He was influential in another case where the outcome is suspect (Clinton is guilty of gross negligence)
All of these mean he *may* have done something untoward.