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
Lenin and Trotsky being as genocidal as Stalin	1917	present	92 years and continuing
Alger Hiss as a communist spy	1947	1998	51 years
Joseph Stalin starving millions	1930?	1980?	50? years
Population bomb hoax	1968	1987	19 years
global warming hoax		present
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
The falsehood of Charles Darwin's theory of evolution	1859	present	151 years and counting
That materialism and evolutionary thought played a role in Hitler's rise to power	1933	present	77 years and counting

|- |The racist Southern Democrats did not become Republicans after LBJ reluctantly passed the Civil Rights Act |1964 |present |53 years and counting |} (please add)