Under what conditions should principle yield to expediency in foreign policy?

As in local politics, so in international: when moral principles are abandoned, other principles, accompanied by appropriate sophistic justifications, take their place. Thus is established power politics, or real politik. And thus can this abandonment of moral principle be traced in the foreign policy of the United States. Analysis becomes categorical, limited to the protection of "vital national interests" by whatever means, and the principles of liberty are factored out and forgotten. But liberty was the first priority for Thomas Jefferson, and our relationship to other nations could not take precedent over that.