I don't know whether the accusations should have been levied, because I don't know the specific content of the law at the time. But on instinct? I think it would have been a terrible case to try and make, given Lewinsky's insistence on it being consensual, even (long) after the fact. Making a criminal case (proof beyond reasonable doubt!) against Clinton that he actually abused his power to get what he wanted...I don't see it happening. It's not even a "He said, she said" scenario. It's a "They both said the same thing but we think she was fooled into it..."
Which leaves us back where we started - he should have resigned, or been made to resign. Because while what he did was probably not demonstrably criminal, it was demonstrably a massive problem (even if you can't prove he used his power and influence to get her to agree to sex, the fact that the possibility
exists and is fairly high should be enough reason to say the relationship was highly innacceptable).
The discussion of specific legal arguments is a little bit pointless because morally everybody can agree that Clinton was guilty and should have been removed from office. When legality is inconsistent with basic, agreeable ethics, legality is in the wrong. So shouting back and forth about whether his obstruction of the truth by pretending he didn't consider oral sex sex is farcical and absurd, and in fact distracts from the much more important discussion, which is what we can do to hold politicians and millionaires responsible who won't be so held by the "justice" system.
Basic, agreeable ethics is not a thing, at least not when it comes to specifics. Even something as simple as "Don't kill" find lots of debate when it comes to specifics. Does it apply to animals? To plants? To enemy soldiers? To people making you feel threatened (stand your ground)? To people actually threatening you (self-defense)? There are lots of different interpretations of where the limits of "Don't kill" are.
The same thing for "Don'T lie". is it acceptable to lie to protect someone? To prepare a (positive) surprise for them? To spare their feelings?
While the basic principles are clear-cut, the specifics of those ethics principles are anything but, and that's why relying on basic principles
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As for "We could all see Clinton is guilty"...the truth is, no, we couldn't. Because Lewinsky, as noted above, still insists the whole thing was consensual, and at some point, "Believe the victim" has to cut both ways - if someone tell you "Actually, I was consenting, not a victim", it's worth listening to them.
That doesn't make the relationship right, but it shifts the problem from "obviously guilty of abuse" to "did dodgy stuff that has the appearance of potential abuse". We don't
know that abuse happened. But the relationship was dubious enough that it should never have happened, and that Clinton should have seen it as a big enough mistake to justify his resignation.