E.J. Dionne (whom I had the privilege of meeting last year and to whom I gave a copy of the New Zealand Prayer Book) writes on Obama's foreign policy for TNR:

Obama is simply paying heed to Reinhold Niebuhr, a thinker admired both by the president and by conservatives. Niebuhr warned that some of "the greatest perils to democracy arise from the fanaticism of moral idealists who are not conscious of the corruption of self-interest" and also that a "nation with an inordinate degree of political power is doubly tempted to exceed the bounds of historical possibilities."

The Obama Doctrine is a form of realism unafraid to deploy American power, but mindful that its use must be tempered by practical limits and a dose of self-awareness. Those are the limits that defenders of the recent past have trouble accepting.