If you are under investigation but you’ve done nothing wrong and you are a Poitician or in a position of leadership, would you care how long the investigation lasted ? Wouldn’t you want the investigators to go above and beyond, leave no stone unturned making sure it was completed thoroughly without question.
I know if it were me I’d want investigators to take as much time as they needed to prove my innocence and to put all accusations to bed. The last thing you or I would want is the investigation to end prematurely only to have our enemies continue their attacks saying the investigation was incomplete or botched. If you’ve done nothing wrong then you’ve got nothing to worry about.
We’ll have to see when Mueller’s investigation is completed, so far based on Trumps behavior he’s done something wrong. It might not be illegal or even immoral but it’s something he doesn’t want to get out. He spends too much time talking about it. He does too many little things that seem to border what appears to some as obstruction.
Consider the Attorney General Jeff Sessions, one of Trumps earliest and the first Senator to publically support him. Once Robert Mueller was appointed to open and lead an investigation Sessions immediately recused himself, it was the only thing he could do. (I can’t stand the fact that Trump has caused me to defend Sessions) If he hadn’t recused himself it would have been a lot worse, the cloud of suspicion would have followed Trump throughout his entire Presidency.
So knowing that and the fact that Trump is livid because Sessions did recuse himself tells us something right there, that dealing with the backlash of Sessions involvement in the investigation is the lesser of two evils, he would rather deal with the backlash than having a complete and thorough investigation.