As much as I hate dragging out this Clinton discussion any further (as I've already done more than enough to drag it out): It comes down to this -

The President was not impeached for having sexual relations in the Oral office (that's not a crime)... The whole aim of that investigation was to embarrass him and probably force him to resign due to scandal...

He was impeached because he committed perjury by lying about the affair in 'court'...

His having an affair was not legal reason to remove him from office... Perjury on the other hand, could have been enough....