When the United States was in its infancy, France experienced a revolution that was in many ways similar to the American Revolution. Some Americans wanted to support the French revolutionaries, arguing that the United States had to pursue its moral ideals and stand by its moral partner. Others pointed out that the American economy was heavily dependent on Britain, the major market for American goods. Moreover, the young country relied on its ability to send exports to Europe, and the waters were controlled by Britain. Whatever moral inclinations the Americans might have had toward France, prudence required that they not take on Britain. The idealists tried to frame their arguments strategically and the realists tried to create a moral cast for their argument, but the problem, in the end, was simple: America's survival depended on not alienating a country that was everything the colonists had fought against.
This argument has constantly torn apart American thinking about foreign policy. Consider this example from the more recent past: In World War II, the United States was allied with the Soviet Union, which was ruled by a genocidal maniac, Josef Stalin. At the time that the United States allied with Stalin, Adolf Hitler was only beginning to climb into Stalin's class of killer. There were those who argued that the alliance with Stalin was a betrayal of every principle Americans stood for. Others, like Franklin Roosevelt, recognized that unless the United States allied with Stalin, Hitler likely would win the war. Those who opposed an alliance with Stalin based on moral ideals certainly had an excellent point -- but those who argued that, apart from an alliance with the devil, the Republic might not survive, also had an excellent point.
Consider a final example. In 1972, the United States appeared to be a declining power. It was losing the war in Vietnam, and its position globally appeared to be deteriorating. The Soviet Union had split from China years before, and their confrontation along their frontier had, on occasion, been bloody. War was possible. Richard Nixon created an entente with the Chinese that was designed to encircle the Soviet Union. In retrospect, the strategy worked. However, in establishing relations with Mao's China, the United States once again aligned itself with a murderous regime. The alternative was an unstoppable Soviet regime.
In each of these cases, the United States confronted this dilemma. On one side was the argument that unless the United States stood for its moral ideals, it would survive but lose its soul. Siding with Britain, Stalin or Mao might have been prudent, but it was a shallow prudence that would eliminate the raison d'etre for the American regime. On the other side was the argument that there could be no moral regime unless there was a regime. The United States did not have the strength to resist, on its own, Britain, Nazi Germany or the Soviet Union. Without such questionable allies, the moral project would be impossible because the United States either would not survive, or would survive as a spent force.
It is important to note that these arguments cut across political and even ideological grounds. In 1972, people on the left celebrated Nixon's alliance with Mao, and it was the right wing that raised moral doubts. Of course, many on the right supported Nixon and some on the left, not taken by the romance of Maoism, were appalled at the alignment. Similarly, it was the left in...