to obstruction of justice. Meaning that he obstructed the process, and wasn't incarcerated for what he did to/with the women. Being charged is one thing--it allows the investigation to proceed in a more thorough, intensive manner. But accusation =/= guilt (for which I am very grateful, given my own personal history).
That's from your own link.
As part of the plea agreement he admitted to non-consensual sexual conduct. Presumably that's accurate--nobody really cares if an admission of guilt is true or not unless they're out to defend the person making the plea or attack the prosecutor and the system as unjust and coercive of defendants' rights. But, again, it wasn't the testimony of the two women that got the guilty plea, but the prosecution in crafting the plea deal. Now, the prosecution may have made that a stipulation pursuant to the accusers' requests, or not. I'm thinking he really was guilty, but that's not the point--the point that I think is being made is that it was just the two women's testimony that was the proximal basis for the finding of guilty and consequent sentencing.
Impeachment is a political process, not a legal process. Arguably he could have been impeached if he had enough people who didn't like him in Congress (or if a few holdouts on really attractive legislation made this a precondition for their vote) and somebody saw him slip into a McDonalds, steal some mustard sachets, and leave without making a purchase. Or was, at least, willing to say so.