You have to think if the CIA seems to think their was some sort of hacking, all people of any party would want this investigated.
That the FBI does not seem to thinks so, shows that both need to bring their evidence (or lack thereof) to the intelligence committee, and sort this thing out.
Why the hesitation?
Trump can say whatever he wants, but he has not been sworn in yet, and why he would be against this, is beyond me.
It just leads to speculation, that he has something to hide, etc.
He could put to rest, with one simple tweet, the word "investigate".