Easy. The media covers for them, lies along with them, and have been so successful at drumming the false "Bush lied" into the minds of the public. Most of them aren't paying attention anyway. They watch the national news and swallow it all hook, line, and sinker.
They would love to start impeachment. It doesn't matter what is true, what matters is regaining power. The very fact that the proceedings were started would send the media into orbit with bashing the President.
notice the word "rhetorical" in the bracket, that's why I put it there.