Jonathan Mercer reviews the evidence against the “credibility” argument:

For their part, the French were indeed worried, but not because they doubted U.S. credibility. Instead, they feared that American resolve would lead to a major war over a strategically inconsequential piece of territory [bold mine-DL]. Later, once the war was underway, Acheson feared that Chinese leaders thought the United States was “too feeble or hesitant to make a genuine stand,” as the CIA put it, and could therefore “be bullied or bluffed into backing down before Communist might.” In fact, Mao thought no such thing. He believed that the Americans intended to destroy his revolution, perhaps with nuclear weapons.

Similarly, Ted Hopf, a professor of political science at the National University of Singapore, has found that the Soviet Union did not think the United States was irresolute for abandoning Vietnam; instead, Soviet officials were surprised that Americans would sacrifice so much for something the Soviets viewed as tangential to U.S. interests [bold mine-DL].

It shouldn’t be surprising that allied and hostile governments saw U.S. involvement in these conflicts in this way. I find it amazing that U.S. policymakers can convince themselves that their credibility is so frequently in jeopardy when it isn’t. Of course, “credibilty” is most often cited as a reason for military action when there are no other credible reasons for war. It is the preferred pretext that hawks use to make unnecessary wars important for U.S. security, and it is a favored tool of demagogues that want to embarrass an administration without taking responsibility for the foolish policy they are supporting. Invoking the danger of lost “credibility” is almost always a scare tactic designed to make people stop thinking about the absurdity of the proposed policy and to worry about other, unrelated problems that will somehow be made worse if the bad policy isn’t implemented.

The Vietnam example is a sobering one. To this day, there are far too many people in the U.S. that believe that the U.S. hurt its position internationally by leaving Vietnam when it did, just as there are today Iraq war dead-enders that think the U.S. should have kept soldiers in that country indefinitely. As far as the would-be defenders of U.S. “credibility” are concerned, the U.S. cannot withdraw from unnecessary wars for fear of appearing to lack “resolve,” and it must launch unnecessary wars in order to demonstrate it. In the end, the fixation on “credibility” is just a bludgeon that hawks use to promote their preferred policies. The fear of lost “credibility” has led the U.S. into several conflicts that it could have easily avoided, and it has prolonged some of the conflicts the U.S. was already in far longer than necessary, yet somehow this false idea holds enormous power over the minds of people in government and the media. If it didn’t, there wouldn’t have been such a surge in pro-war commentary over Syria that relied so heavily on this unfounded belief in the importance of “credibility.”

P.S. Mercer makes a relevant comment on Syria later in the article:

Those who argue that reputation and credibility matter are depending on strategists to be simple-minded, illogical, and blissfully unaware of recursion. And if Assad is illogical, then calibrating U.S. foreign policy to elicit particular responses from him is pointless.