The problem with impeaching him is that is exactly what he wants to happen. You impeach the first Black President (ok really the second one) and you galvanize the last large block of voters he has left.
Not to mention there is no guarentee that with a GOP majority in the Senate you'd get 2/3rd's of them that would convict.
Then you'd have the media trashing the GOP (again) about a witch hunt just like they did with the Clinton impeachment.