Origin: 1966
In war, truth is the first casualty. That maxim seemed evident as the United States mired itself deeper and deeper in the Vietnam War and protests at home became correspondingly more strident. As President Lyndon Johnson attempted to finesse the failures of the war by escalating our involvement and putting on a face of increasingly unfounded optimism, he fell into what would be called a credibility gap.
The term was used in the headline "Dilemma in 'Credibility Gap'" in 1965, but it became widely understood and discussed in 1966, after a December 1965 Washington Post story referred to "growing doubt and cynicism concerning Administration pronouncements.... The problem could be called a credibility gap." Soon pundits of various shades, as well as political opponents, were gaping at the gap.
Unpopular in part because of the credibility gap, Johnson, who had won so handily in 1964, did not even try for reelection in 1968. But though Johnson retired, credibility gap did not. It was used in 1970, for example, by an African-American leader declaring that President Nixon's administration "faces a credibility gap of enormous proportions" with blacks.
Other gaps have also been discovered in twentieth-century America. There was the missile gap, a Democratic complaint against the Republican administration in the late 1950s that the United States had not kept up with the Soviet Union in production of intercontinental ballistic missiles. We have also spoken of a generation gap (1967), "differences in values, goals, and attitudes between younger and older generations," and the gender gap (1977), "differences in values, goals, and attitudes between men and women."