If he should be in jail, then why isn't he in jail? If they have something on him for ****s sake then actually arrest and charge him. Sentence him and do it. Lord knows they've tried.
Because about 3/10 of the country is going to go absolutely apeshit when they do arrest him. In fact, that's probably the only reason they haven't. Well, there are two. One, we don't go around jailing our political opponents in this country. Two, there'd be more demonstrations with open carry or riots without than you could shake a stick at. The DoJ is in a terrible position here. He's probably guilty as all get out and they're really handcuffed by exigent circumstances.
Let's say this: asserting that since he hasn't been arrested because he hasn't been arrested is begging the question. You're committing a logical fallacy. It's evidence that can't be released, so it sits in the shadow of darkness. How serious the offense? "Well, we can't release that." Why? "Because that would compromise national security and put Americans in death's way."
There are no good solutions to this. They can't willy-nilly arrest the guy because there's a thacket of problems that goes along with that. Surely this must have occurred to you.