I first noticed George W. unable to pronounce the word nuclear, when he was in office. But now I am hearing nucular from various media commentators.
Was it 'W' who started it ?
[Note: I worked in the UK nuclear industry (making products for medical research and cancer treatment) from 1986 to 1994 and I never heard the word 'nucular' once.]
The answers in the linked question provide a good analysis of how such a pronunciation might have developed. There are other sources with insight into that question as well.
As for when: The pronunciation /ˈn(j)ukjələr/ and in fact even the spelling "nucular" date back about as far as the term was widely used in the general public, in the mid-20th century.
The OED even provides a definition for the spelling:
Alteration of nuclear adj., representing a colloquial pronunciation (widely criticized by usage guides)
The earliest attested use, as mentioned, is as early as 1943 in printed form, though the citation is surprisingly not from a popular publication referring (as one might guess in the 1940s-'50s) to nuclear weapons, but rather is found in a scientific periodical.
They..begin the reversion process which results in a 4n restitution nucleus... A nucular membrane begins to form around the whole group or around smaller groups or isolated chromosomes.
OED notes that it used to be discouraged, but offers no judgment on the form:
it is now commonly given as a variant in modern dictionaries. See Webster's Dict. Eng. Usage (1989) 673/1 for a discussion of possible origins of the pronunciation.
