Good point. Obama was emailing her regularly on an unsecured server using a fake name. He LIED that he 'found out about her email server through news reports.' Flat out LIED to the American People. And since he knows that 100% of all Presidential communications are considered to be classified until they're been analyzed and released, he's guilty (as is she) of knowingly violating Federal Law.
I think Comey realized how he screwed up the first go around and seeing Trump's momentum, decided he should "reopen the case" just in case he needs to tell his new boss 'we're working on it.'
If she winds up getting elected, he can easily say, 'We found nothing."