It's an innocent mispronunciation for most
For Bush, I think he did it to sound more folksy. And today, those on the Right who say it, do so to be anti educated.
Nuclear technology seems complicated and the luddites in the GOP consider anything complicated to be the educated elite. Notice how Trump throws it into speeches often because he had an uncle who was an engineer. It's an appeal to expertise fallacy. "My uncle did this job that you don't understand, so I'm smart..." Trump's uncle was actually an electrical engineer who taught at MIT and did write about nuclear physics and founded a company that worked on nuclear medical technology. His business collapsed when the government cut his funding.
But at its core to this brand of fascists in charge right now, it means, "leave the complicated stuff to us, we get it, and we'll handle it for you. Don't let those educated elite libs tell you how to pronounce words."