This is how *real* federal investigations work. They grind and grind and grind until they get to the grist. It's not uncommon for a fed investigation go to five or six years. The only thing that speeds them up is if they have to charge someone to be the statute of limitations (like Sussmann.) DOJ US attorneys don't take any chances. When they give you a subpoena or execute a search warrant, they aren't looking for the evidence you have. They already have it. They are looking to prove either than you had it the whole time, or that you destroyed it (spoliation). It's the DOJ culture. They are apex predators. They don't risk the political cost of charging someone unless they KNOW they can convict them. That he is going after the campaign itself means that he KNOWS he can convict at least some members of the campaign. He probably will never charge Hillary because he doesn't know he can convict her (not because of facts but because of jury nullification.) But he might be able to take down everyone around her and leave her powerless.