Why Bush isn't impeached?

I've notice a huge contradiction in our political system. George Bush Jr has lied to the American people about WMD's, and now we are in a full scale war over the obvious truth, oil! And no one ask for him to step down, but yet Clinton is impeach for a ******** and Elliot is forced to step out of office. However Bush goes untouched, even with a threat of recession. What's up with that?