Goodhart was an economist and Campbell was a social psychologist. The fact that they independently made similar observations in different fields is substantial. Though, maybe it's more efficient to remember the over-arching idea, it also makes sense to identify them independently.

I agree they are basically saying the same thing but there is a subtle difference. Goodhart is observing a fact about measures, Campbell is offering an explanation of Goodhart’s observation, that is, why the target ceases to be a good measure. Goodhart is making a very general observation which might be true for a number of reasons. One alternative to the Campbell version is that value of a measure ages so, by the time the measure has become a target, the world has moved on and the target isn’t any good.

There's a difference?

> I infer an undercurrent of “politics is about manipulating people not representing them”

There's a scene or two in The Wire about "Juking the stats" (1) - its about fooling the people in order to look good and meet campaign promises. Manipulating indeed. More like "Mayor Carcetti's going to juke himself a second term"

> “Wally is going to code himself a minivan” (Dilbert ref) from Goodhart

Not really, Goodhart was talking about UK monetary policy in 1975. It's political from the start. (2)

These aren't different.

1) https://medium.com/@roshanrevankar/juking-the-stats-5926eaf5...

2) "Goodhart's law is an adage named after British economist Charles Goodhart, who advanced the idea in a 1975 article on monetary policy in the United Kingdom, Problems of Monetary Management: the U.K. Experience:

Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes."

(Wikipedia)