Obama debuted on the political scene with an atmosphere of messianic excitement. A July 2008 column by Mark Morford in the San Francisco Chronicle asked, with no detectable sarcasm, whether Obama was a “Lightworker” — described as “that rare kind of attuned being who has the ability to lead us not merely to new foreign policies or health care plans or whatnot, but who can actually help usher in a new way of being on the planet.”

These moments, when self-righteousness shines from every pore, are probably when politicians should be most careful — and since they rarely are, these are the moments when the public should be most vigilant. For almost every scandal is rooted in the belief that what you and your allies are doing is so good, so noble and so necessary that it can justify some moral shortcuts.

The Contras really needed those arms. A President is entitled to a little canoodling with an intern, and it’s acceptable to lie under oath about it. To quote Nixon, “When the President does it, that means that it is not illegal.”

Good screenwriters know every villain believes he is the hero of his own story. The human capacity for self-justification can be pretty epic even outside a highly charged political atmosphere in which each side sees itself as the living embodiment of everything that makes America great — and the other side as a motley amalgamation of petty, corrupt, selfish special interests.