The maximum sentence for a crime is defined by statute, rather than being some special threat by prosecutors. For wire fraud it's 20 years, even if your fraudulent scheme was designed to enrich you by only $1. Sentencing is determined by the court after conviction; it's unlikely that he would have been sentenced to more than a couple of years.
This thing of focusing on the maximum possible sentence is a bad habit inculcated by the media. It's more instructive to look at the median sentence for this kind of crime.
You forget the Federal Sentencing Guidelines. His level, minus enhancements, based on $5 million fraud, (according to the indictment) yields a sentence of 57-71 months plus 2-3 years of supervised release (no computers) plus a fine. That's a good deal more than, "a couple of years."
That's what you get for having elected prosecutors. But quoting the statutory maximum as a matter of fact for a soundbite and asking the court to impose it (which it seems they were not about to do) are very different.
That's true, but they are political appointees and most have been have pursued the path of running for DA or attorney-general in state and local elections. Sorry for the confusion, I suppose I should have said that the trouble was that the office of prosecutor is political (as opposed to professional) in the US.
It is expressly not (supposed to be) political, but how you interpret that is up to you. See: Monica Goodling, Tim Griffin, et al. As far as aspirants to elected office goes, Giuliani is a rarity among federal prosecutors more than he's an exemplar, most are lawyerly lifers. It's like saying kernel hackers are secretly pining to become marketing executives.
If my lawyer told me that the threat was garbage and that I'd be able to get a plea bargain somewhere between a few months and nothing at all for something I did purely out of civil disobedience, I wouldn't exactly kill myself.
All I can say is that some people aren't cut out for prison, and there was no indication that "nothing at all" was a possible outcome, save one's faith in the jury system.
However, my point was to note the contradiction in you saying that prosecutors can't be swayed by emotion, while they conduct themselves so as to sway their targets with same. If you don't think that the threat of a long prison sentence would spur emotion in the person receiving the threat, well, I don't know what to say.