This role reversal is a case study in the awesome power of the partisan mindset. Up to a point, American politics reflects abiding philosophical divisions. But people who follow politics closely — whether voters, activists or pundits — are often partisans first and ideologues second. Instead of assessing every policy on the merits, we tend to reverse-engineer the arguments required to justify whatever our own side happens to be doing. Our ideological convictions may be real enough, but our deepest conviction is often that the other guys can’t be trusted.