As they obviously understood due process and right to a fair trial, even if you don't. We certainly don't have US Civil trials with Russians, British and French judges, so Nuremberg would seem irrelevant to US trials..........again if your arguing Lincoln and Johnson were criminal, or were Chase, Evarts, or Dana Jr were in their actions or opinions provide it........though I have seen nothing that suggests they were, or that they were not qualified. and indeed it was their responsibility to make the decisions.
That you disagree in favor of what ifs, not does mean they were wrong, or the course they took wàs wrong. It certainly does not make any of your what ifs put forth true.
The simple reality is there were qualified men, both political and legal on hand, more then familiar with existing interpretations and moods, and whose role it was to decide how best to proceed legally, and how to best proceed politically. And they in fact did.
All this smoke and mirrors doesn't change that at all. So I indeed note the historical reality, and see little evidence for a reason to second guess their decision.......
Instead I agree with them proceeding had risks of negative effects either if they won or lost......and tangible benefits from if successful seem non-existent.