As has been stated though, the FBI doesn't usually publicly comment on the status of their investigations.
Since the only thing to report was pursuing a warrant for access to the emails under the previous investigation, it's hard to see it as anything but political at this time.
There's no legal justification for it. There's no specific material they are able to release or comment on. There's not even a timeline.
So why the letter and announcement to congress (let alone the letter justifying his actions to his underlings)? Hard to see it as anything but politics, whether on the national scale or institutional.