Comey can not summon a grand jury. Federal prosecutors do that.
Here’s Andrew McCarthy on the subject:
http://www.nationalreview.com/article/430211/hillary-clinton-email-fbi-department-justice-obama
...The FBI does not have authority even to issue subpoenas, let alone to charge someone with a crime. Only federal prosecutors may issue subpoenas, on the lawful authority of the grand jury. Only prosecutors are empowered to present evidence or propose charges to the grand jury. And the Constitution vests only the grand jury with authority to indict — the formal accusation of a crime. In our system, the FBI can do none of these things.
No Justice Department, no grand jury. No grand jury, no case — period. As a technical matter, no matter how extensively the FBI pokes around on its own, no one can be a subject of a real investigation — i.e., one that can lead to criminal charges — unless and until there is a grand jury. That does not happen until the Justice Department hops on board...
Thanks!!
...Interesting tho that the talking heads did not do their homework on the subject.