At his ever-interesting blog Done With Mirrors, Callimachus offers the definitive explanation of why George W. Bush says "nukular" for "nuclear," (as opposed to GW's own father, who pronounces the word conventionally).
Apparently, GW is just following precedent for many Presidents, and even some nuclear (that is, nukular) scientists:
It's not exactly correct to say the president mispronounces the word. He uses an alternate pronunciation -- "nu-ku-lar" -- that might be considered dialectal. It is commonly heard in the U.S. South, and in the U.S. military (which traditionally draws disproportionately from the old Confederacy states). Its use has been noted since the early 1960s among nuclear scientists themselves, including British and Canadian scientists.
Bush is not the only modern president to say it that way. Oddly, his father wasn't among those who did (though he had his own grating way with Sa-a-addam). But Bill Clinton and Jimmy Carter, both Southern men, said "nu-ku-lar." So did John F. Kennedy and Gerald Ford, who perhaps picked it up during their military service.
The first U.S. president we know of to say "nu-ku-lar," and the first to be widely scolded for it, was Eisenhower, as far back as his "Atoms for Peace" speech to the UN....
According to Callimachus, it turns out the Bush isn't stupid, he's lazy--lazy of tongue, that is. This type of laziness has been common to vast numbers of human beings throughout time, and has contributed greatly to the growth and evolution of language. The process by which nuclear becomes nukular even has a name; it's called metathesis by linguists. The same process has given us such tried and true favorites as "dirt" and "fright."
So, George Bush's pronunciation may really be progressive--although don't tell that to any actual self-labeled "progressives." In fact, it may even be evolutionary.