He wasn't impeached for getting dirty in the Oval Office with Monica; he was impeached for lying about it.
Bingo! Even worse: for PERJURING himself about it.
What's interesting is that neither he nor the liberals seem to get that. Of course, he also lied about cutting taxes in his '92 campaign. He excoriated Bush41 for "the largest tax hike in history" and then push Congress to raise taxes. And his liberal supporters said, "Well, of course! He HAD to lie about that to get elected."
Lying doesn't count if you're a liberal.