In non-political terms, what is a post-turtle?

It’s a political thing.

(Because it’s funny:)
Post turtle is a phrase that has been used in political discussion of various countries,
including the U.S. and Canada, based on an old joke.

The joke:
An old rancher is talking about politics with a young man from the city. He compares a politician to a “post turtle”. The young man doesn’t understand and asks him what a post turtle is.
The old man says, “When you’re driving down a country road and you see a fence post with a turtle balanced on top, that’s a post turtle. You know he didn’t get up there by himself. He doesn’t belong there; you wonder who put him there; he can’t get anything done while he’s up there; and you just want to help the poor, dumb thing down.”
-Wikipedia