I'm only half embarrassed that this somehow didn't occur to me. My initial read was that there's probably some personalities who would have gotten a kick out of recording a message... but it (sadly) doesn't make a lot of sense that Richard Nixon would make fun of himself in such a casual way.

Still, I appreciate how a lot of these make me feel. Simpler time!

I'd say the fact that Popeye has one is a dead giveaway

I assumed they were impersonations. But if they aren’t, it could be the real person who did the popeye voice, so not a giveaway after all.