From where I stand, I think the IC (under leadership of the FBI) have already enough evidence (legally binding).
The problem is that they do not have a prosecuting body that they can take the evidence to. Because that would need to be Congress, which does not (yet) have interest. From the way they behave, one of the most probable explanations is that key members of GOP are complicit (or at least have knowledge of, and try to block, which in itself is illegal) in the criminal actions under investigation.
From what I see, the only way out is what is termed a "social media impeachment" in which irrefutable evidence is presented in a public, legally binding and recorded forum, such as a public court trial or public congressional hearing. This is what Comey intended, and still intends to do -- from what I hear, the reason he was scheduled to appear before a committee coming Tuesday, but was canceled, because he insisted on a public hearing. See, he already told people enough in non-public hearings, but nothing happened.
The reason he waited so long, IMO, was to collect enough evidence that would stand up in such a forum, or was admissable outside of congress in a suitable court in a trial against someone sufficiently down the ladder to prosecute, but not low enough to block evidence against the big fish, and was convincing enough to blow the **** far enough.
