On the bottom line(http://lesswrong.com/lw/js/thebottomline/)/[politics as a mindkiller:

This is a practical country. We have ideals; we have philosophies. But the problem with any ideology is, it gives the answer before you look at the evidence. [Stewart: Right.] So you have to mold the evidence to get the answer that you've already decided you've got to have. It doesn't work that way.

Source: Bill Clinton, in an appearance on The Daily Show with Jon Stewart (episode date: September 20, 2012). The quoted material appears at about the 6:50 mark.