“He should be supported or opposed exactly to the degree which is warranted by his good conduct or bad conduct, his efficiency or inefficiency in rendering loyal, able, and disinterested service to the nation as a whole.
“Therefore it is absolutely necessary that there should be full liberty to tell the truth about his acts, and this means that it is exactly as necessary to blame him when he does wrong as to praise him when he does right.
“Any other attitude in an American citizen is both base and servile.
“To announce that there must be no criticism of the President, or that we are to stand by the President, right or wrong, is not only unpatriotic and servile, but is morally treasonable to the American public.
“Nothing but the truth should be spoken about him or any one else.
“But it is even more important to tell the truth, pleasant or unpleasant, about him than about any one else.”
-Teddy Roosevelt, “Lincoln and Free Speech,” The Great Adventure (vol. 19 of The Works of Theodore Roosevelt, national ed.), chapter 7, p. 289 (1926).
Big thank you to darkstar for pointing this out.