Alternate meaning: The Credibility Gap, comedy team

Credibility gap is a political slogan, originally used in the New York Herald Tribune in March of 1965, to describe then-president Lyndon Johnson's handling of the escalation of American involvement in the Vietnam War. A number of events—particularly the surprise Tet Offensive, and later the 1971 release of the Pentagon Papers—helped to confirm public suspicion that there was a significant "gap" between the administration's declarations of controlled military and political resolution, and the reality. The term was later applied to the discrepancy between evidence of Richard Nixon's complicity in the Watergate break-in and his repeated claims of innocence.

"Credibility gap" was, itself, a takeoff on the phrase "missile gap." This phrase was used repeatedly by John F. Kennedy during the 1960 presidential campaign to criticize the Republicans for their complacency in regard to supposed Soviet ICBM superiority. One month after Kennedy took office, he apparently discovered that the missile gap did not exist. The U.S. was, in fact, far ahead. The "missile gap" was revealed to be the product of exaggerated and possibly self-serving Air Force reports, and was spoken of no more. Thus, the phrase "credibility gap" referred back to Kennedy's credibility problems with the "missile gap."

In modern times, the term has come to be used by political opponents in cases where an actual, perceived or implied discrepancy exists between a politician's public pronouncements and the actual, perceived or implied reality.