The investigation has been going on for 10 months now, if there was anything of substance against Trump they would know it by now. Dragging this out seems to be designed to hurt Trump intentionally.
It would only take a couple months to get all the phone records, travel reports emails, etc and look for any collusion between members of Trump’s team and Russian Government, if they have not found anything of substance by now, they won’t.
The FBI and our various intelligence agencies are openly leaking all classified information that can hurt Trump, even releasing transcripts and recordings of his private conversations with world leaders. At this point if there is even the slightest shred of evidence against Trump we would have seen it leaked to the press by now.