I don't understand how he could have been impeached but did not have to leave office.
Bill Clinton was acquitted. The senate did not reach the 2/3's majority needed to fully process his impeachment.
To further break it down.
Clinton was impeached by the House on two charges. The first being perjury, and the second being obstruction of justice.
Following this he was acquitted by the senate.
The "impeachment" process takes place in two steps.
First, a President has to be impeached in the House of Representatives. that is the equivalent of an "indictment."
Then, the President is tried in the Senate, with the Chief Justice of the United States presiding. It requires a two-thirds vote of the Senate to remove an impeached president.
President Clinton was impeached in the House (on two counts) but not removed by the Senate. Ditto for President Andrew Johnson (who survived by one vote). President Nixon resigned before the impeachment was completed in the House because it was clear that the Senate would have voted to remove him had the proceedings gone that far.
Put another way, President Clinton was "indicted" (impeached), tried, and acquitted. The "acquitted" part meant that he did not have to leave office.
Simply put, Bill Clinton WAS impeached. The impeachment process is similiar to a Grand Jury in which the House stands as the jury and decides whether or not sufficient evidence of a high crime or misdemeanor is sufficent to turn it over to trial in the Senate. So yes Bill Clinton WAS impeached...but the Senate accquitted him so he was not ousted from office.
Interestingly enough, the charges - which was perjury (lying under oath) - were enforced by the judge of the trial in which he lied. Bill Clinton was fined and lost his license to practise law.
So while he was not punished by the Senate, the judge DID enforce the charge...which BTW WAS true...the court transcripts were proof of that.