"Credibility" has long been a preoccupation of American geo-politicians.

Though never clearly defined, its primary meaning for Washington has been the need to demonstrate our persistent will to defend American policies throughout the world.
From the first days of America's emergence as a superpower, our leaders have normally acted as if U.S. credibility depended less on truthfulness than on an image of or the exercise of raw military strength.

Beginning early in the Cold War, presidents, national security advisers, and nuclear strategists insisted that credible threats to use force were essential to protect vital U.S. interests whenever and wherever they were challenged.
In Vietnam, American leaders prolonged the fighting not so much out of confidence that their objectives in that small,
distant country could be achieved, but out of a fear of losing and thus sapping our "global credibility."

The phrase "credibility gap" first entered American political vernacular in 1965, in the middle of an era of "gaps" (from the "missile gap" to "the generation gap"). Journalist David Wise used it to highlight the gulf between President Lyndon Johnson's claim that American military escalation in Vietnam was limited and defensive and an emerging public perception that it was, in fact, massive and aggressive. In light of the current situation, it is important to recall that the Vietnam-era credibility gap took years to form and did not become a Grand Canyon until the Nixon years, late in the war, after some 35,000 Americans and at least a million Vietnamese had already died.
Farce, Charade, Deception