Reply #28: It's a very common pronounciation error, even in many very intelligent people.

[Odin2005]

LBJ and Carter pronounced it "nukular," too. It seems like many English speakers have a problem with the k-l consonant cluster as it in "nuclear," our brains for some reason want to switch around the l and the e, and then turn the e into a reduced "schwa" vowel. Something similar, a process called "metathesis," is the cause of the mispronunciation of "ask" as "aks," a mispronunciation that, amazingly, goes back to Old English, where you kind the word written as either "Ascian" or "Acsian".