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

|
|
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Piltdown Man hoax  | 1912  | 1953  | 41 years
Lenin and Trotsky being as genocidal as Stalin  | 1917  | present  | 102 years and counting
Alger Hiss as a communist spy  | 1947  | 1998  | 51 years
Joseph Stalin starving millions  | 1933  | 1986  | 53 years
Population bomb hoax  | 1968  | 1987  | 19 years
global warming hoax  |  | present  |
Effectiveness of supply-side economics | 1975  | present  | 44 years and counting
How Reagan caused the fall of communism | 1991  | present  | 28 years and counting
Harm caused by the New Deal during the Depression  | 1933  | present  | 86 years and counting
The falsehood of Charles Darwin's theory of evolution | 1859  | present  | 160 years and counting
That materialism and evolutionary thought played a role in Hitler's rise to power  | 1933  | present  | 86 years and counting
The racist Southern Democrats did not become Republicans after LBJ reluctantly passed the Civil Rights Act  | 1964  | present  | 55 years and counting

(please add)