1. The facts as they are PUBLICLY known to the players involved (Trump, his legal team, his political advisors, the DOJ, the House and Senate committees overseeing these matters, etc.)
2. The facts as they are ACTUALLY known to the players involved
There is an important distinction between the two, and this requires events to unfold in a way where #2 will always precede #1. In effect, the players involved have to "play dumb" because they may be privy to a lot of information that they can't discuss in public until it is out in some kind of public domain.
The Sen. Grassley letter from a few days ago where he requests a number of documents and answers to a number of questions from Deputy AG Rosenstein is a perfect example of this. Grassley knows the answers to all of the questions he asks in that letter. But he still has to go through the process of extricating the information from Rosenstein's office because none of it can be used in a legal process until it becomes "public."
This is exactly what Trump is doing here. He knows what happened, but he has to get the information out in the open through a venue that actually has legal authority to do something with it. An investigation of the FISA abuse should have started a long time ago (it may have already started), but the trickle of information into the public domain in recent weeks gives Trump more credibility to pursue this course of action than he would have had several months ago.
Ugh... the public doesn’t have to know all the evidence in a criminal case before indictments. Perhaps what you are implying is that in political situations the public needs to have the information in front of them in order to understand the actions Trump is taking.