Re-opened, and did so quick enough to re-close it before the election, although claiming you reviewed thousands of emails in a couple weeks is sketchy. It's plausible that Comey thought failure to handle the new evidence on Huma Abedin's laptop would undercut his next boss and wanted it out of the way, and that he misjudged how people would react to it and/or overall odds of her winning. Almost everyone thought Clinton had it locked up. If they had ignored it until after the election and it came out, that would have been at least as much of an issue for her as the russian collusion claims were for Trump, or worse since she absolutely did mishandle classified intelligence. There is no 'extremely careless' exception in the law, just gross negligence. There SHOULD be a mens-rea requirement in white collar work, and on those grounds I could kind of approve of not charging her IF they applied the same standard across the board. They don't.