"The President is merely the most important among a large number of public servants. 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 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."
---Theodore Roosevelt in the Kansas City Star, May 7, 1918
Here's part of a Slate article you might use to help search for quotes and context:
http://slate.msn.com/id/2080735Dissenters spoke out against virtually every subsequent conflict. The humiliating defeats of the War of 1812 made that fight so unpopular that the states of New England considered seceding from the Union.
A generation later, many Americans viewed the Mexican-American War (not unreasonably) as an act of naked U.S. aggression. In 1848, shortly after the war's conclusion, Congress censured President James Polk for "unnecessarily and unconstitutionally" commencing hostilities. Supporting the rebuke was Illinois Rep.
Abraham Lincoln, who attacked Polk as
"a bewildered, confounded and miserably perplexed man." (hmmm, maybe * has a competitor for Worst President Ever--JHB)
Popular support for the Spanish-American War waned as the relatively easy fight for a free (i.e., pro-American) Cuba gave way to a more controversial program of wresting away Spain's other colonies, particularly the Philippines. When President William McKinley opted to annex the Philippines—he wanted, he said, "to educate the Filipinos and uplift and Christianize them"—a motley array of critics from Andrew Carnegie to Mark Twain objected. William Jennings Bryan used his dissenting stance as the centerpiece of his (losing) 1900 presidential campaign.
During World War I, critics excoriated Woodrow Wilson—who had run for re-election in 1916 on the slogan "He kept us out of war"—for entangling America in a bloody European conflict. Political leaders from Wisconsin Sen. Robert LaFollette to Socialist Party presidential candidate Eugene V. Debs spoke out. ("I had supposed until recently that it was the duty of senators … to vote and act according to their convictions," LaFollette sardonically told the Senate. "Quite another doctrine has recently been promulgated by certain newspapers … and that is the doctrine of 'standing back of the president' without inquiring whether the president is right or wrong.") The majority of Congress, however, passed a series of repressive laws that let the government imprison or deport thousands of critics of the president, including Debs. Vigilante groups ostracized, assaulted, and even lynched countless more.
In fact, the only major war that lacked an organized bloc of dissenters was World War II: Pearl Harbor had made an isolationist stance untenable, and as Americans learned more and more about Nazi Germany, most anti-war activists decided the defeat of fascism was worth fighting for. (Some rejoined peace movements, such as the nascent anti-nuclear effort, at the war's end.) Still, even during the "Good War," critics persisted. On the left, pacifists served prison time for refusing to fight or perform compulsory alternative service.
On the right, congressional Republicans launched an investigation of Pearl Harbor, with some implying that Franklin Roosevelt had foreknowledge of the attack.