Clinton was impeached because he lied to the Grand Jury. Yes, what he lied about was his affair with Monica but he was impreached because he LIED, not because of his affair. The President of the US is supposed to uphold the laws of the US and by lying to the Grand Jury, he didn't do that and was impeached.
Personally, I think Congress failed the entire nation when they didn't boot his lying a$$ out of the Presidency.
Looking back at history, if they would have booted him out, Gore would have become President for that term and "maybe" would have won the next election.
But, things didn't work that way and I'm sure glad Gore lost!!!