Longest liberal denials

Liberal denial is a familiar phenomenon. What are the longest liberal denials in history? Here's a growing list:

Denial	Beginning of denial	Ending of denial	Length of denial
Piltdown Man hoax	1912	1953	41 years
Alger Hiss as a communist spy	1947	1998	51 years
Joseph Stalin starving millions	1930?	1980?	50? years
Population bomb hoax
global warming hoax
Effectiveness of supply-side economics	1975	present	34 years and counting
How Reagan caused the fall of communism	1991	present	18 years and counting
Harm caused by the New Deal during the Depression	1933	present	76 years and counting
That Christian Anti-modernists are Anti-Semitic	at least 1973	present	35 years and counting

(please add)