Cause-effect brain teaser: Optimists, Republicans and libertarians

According to the Associated Press...

Views of the economy show sharp partisan differences, with Republicans far more likely to be optimistic than either Democrats or independents, according to the Pew Research Center for the People & the Press.

Sounds as if Pew Research is finding that optimism is highly correlated with people who lean Republican (...and, I strongly suspect, libertarian).  Although correlation doesn't necessarily imply causation, it obviously doesn't deny it, either.  Now I'm wondering, if there is causation, which direction does it go?

Although it's no surprise to me that pessimism and Democratness apparently go together (...they always seem to be hoping and searching for economic bad news, and energized when they find some), I wonder if the cause/effect for optimists is:

(a) if Republican/libertarian, then optimist; or
(b) if optimist, then Republican/libertarian. 

Food for thought, that's all.  (And before jumping to any conclusions about which label I deserve, please read this list of things I'm not.)