It was precisely because: 1) Gerald Ford pardoned Richard Nixon "from all crimes past and present" (and turned over the vast majority of the incriminating "Watergate Tapes" back to Nixon where they were kept secret and never publically revealed), and 2) Bill Clinton put a halt to four separate Congressional and justice dept. inquiries into the Iran-Contra matter, the 1980 October Surprise, and other illegalities involving George H. W. Bush, that no government accountability occurred, and we then had a repeat of these type of tragic serial abuses of power and War crimes again in 2001 - 2008. In fact, the political careers of any of George H. W. Bush's sons may have been impossible had George H. W. Bush himself been held accountable in the first place.
Did at any time, Dick Cheney or George Bush fear prosecution? No, and they had no reason to, because of the past precedent, which Obama now appears set on repeating.
When I was younger, I used to think 'well, at least we'll never have another Vietnam War ever again', but I was wrong about that because nobody ever prosecuted Lyndon Johnson or the CIA for the deceitful "Gulf Of Tonken" manipulations that led to the fullbore US Ground & Air Invasion/Occupation. Nobody ever prosecuted Nixon for his bombing raids, his public misrepresentations, and his attacks against law and civil liberties, and other abuses of democratic processes.
So, Cheney and Bush knew that they had nothing to really worry about. Just mere troubling political perceptions by themselves can be easily "managed" and mitigated by the right-wing noise machine. They knew that nobody would ever actually touch them.
This is why Obama is making the wrong decision here. He does need to focus on the past, in order to protect the future.
Because one day in the future, there will be a President Jeb Bush, or a President Rudy Gulliani, or whomever -- and the same damn criminal policies will just be repeated all over again.
Our poor Country has already now had our second "Vietnam" and worse.
It is time to put a stop to this madness.
The U.S. Constitution and The Bill Of Rights are not "optional" documents.