The FBI had to do this. The Trump campaign is making all kinds of threats of election rigging and its post-poll consequences. This was going to come out and it's better for Clinton that it comes out now. There's still plenty of days for this to die down. And die down it should. Eminent US politicos of all colours have tried to control their emails via private servers since emails were invented. There may be differences in scale and content, but they're all at it, except for Trump of course, who's immune from this because he hasn't been in politics. Email is not a secure medium and they shouldn't be doing this, but they all do, hey bloody ho. A quick smacky botty then move on.