This letter of resignation (New York Times) written by a U.S. ambassador to Colin Powell is eloquent and earnest.
bq. Mr. Secretary, I have enormous respect for your character and ability. You have preserved more international credibility for us than our policy deserves, and salvaged something positive from the excesses of an ideological and self-serving Administration. But your loyalty to the President goes too far. We are straining beyond its limits an international system we built with such toil and treasure, a web of laws, treaties, organizations, and shared values that sets limits on our foes far more effectively than it ever constrained America’s ability to defend its interests.
bq. I am resigning because I have tried and failed to reconcile my conscience with my ability to represent the current U.S. Administration. I have confidence that our democratic process is ultimately self-correcting, and hope that in a small way I can contribute from outside to shaping policies that better serve the security and prosperity of the American people and the world we share.
A lot of people have been expressing such sentiments for a while now. I hope that John Brady Kiesling's thoughtful remarks are heard somewhere that matters.