Everyone is on about how Comey saved Hillary from prosecution, but everyone is missing the larger picture: by acting in this purely political fashion, Comey saved the entire entrenched oligarchy from prosecution.
Remember how the Trump University trial was originally scheduled to begin July 7, the same day the Republican convention was to start? Well, that changed in May. Trump used the existing rigged judicial system to get the trial date moved to November 28. Trump can't have an embarrassing trial take place at an economically or politically embarrassing time, now can he? Trump is too big, too important, to be troubled by picayune little fraud trials. Better for all concerned if no little people stood in the way of his ambitions. So, in May, even as the trial judge is moving the trial date, Trump deflected attention to the way the system is rigged in his favor by ... wait for it... complaining that the system is rigged against him.
Now that Comey has declared Clinton off-limits to the law, now that the rigging of the system is on display for all to see, Trump has the complete deniability he has always claimed. By declaring Clinton off limits, Comey has declared every last one of the oligarchs safe.
You see, no matter who tries to bring Trump to trial, Trump can now say "It's all political! It's a rigged system! That's why they are after me! I'm pure as the New York slush!" By clearly showing the world exactly how rigged the system is, Comey has effectively denied the validity of every trial motion that could ever be brought against any of the oligarchs. Oligarchs can never again be convicted of anything.
Every powerful person can use the Trump-Clinton-Comey defense ("The system is rigged against me!") no matter what the situation may be. The oligarch's sycophants will then take up the chant and shout down whoever points out that the evidence of guilt is actually quite clear. Every trial can now be reduced to a political witch-hunt, every shred of evidence is just an irrelevant fact blown out of proportion by people out to get the oligarch, no reasonable prosecutor would ever use such tainted material, and if any prosecutor ever did, that person is, by definition, on a McCarthyite witch hunt.
By illuminating how rigged the system is, Comey has declared every oligarch with sycophants and a power base (which is all of them) off-limits.
What we saw done successfully as a one-off tactic with Ken Starr and Bill Clinton has now been turned into federal policy. We are officially a banana republic. Trump and Clinton couldn't be happier with how this has turned out. It's a win-win for the nation! We should be thanking Comey: he has finally made America safe for oligarchs.