In the typical election, we hear that the market is strong (weak), that is a positive (negative) for the incumbent and that we can see the results in the challenger's rising (falling) poll numbers.
This sort of analysis is muddled.
The proper way to put this into context isn't to think of this as a causal relationship between two variables; rather consider these two variables -- markets and polling data -- within a much more complex dynamic system.
For a moment, imagine that the incumbent of either party is enjoying a robust recovery. People are working, unemployment is low, wages have risen, consumer spending is brisk, corporate profits are strong and rising. All of these should help both the stock market, and the incumbent’s party.
Conversely, during a recession, we see the opposite happen: Unemployment rises, consumer spending falters and profits are declining. These factors hurt the market, and that hurts the incumbent’s poll numbers.
It isn't that one factor causes the other; it's that they both are affected by the underlying strength or weakness of the economy. (I’ll save the discussion about how we give presidents too much credit and blame for another day).
Getting this mixed up is a very common error. It is why I have said repeatedly that politics and investing don’t mix.
So go ahead: Listen to what the pundits have to say. But see it for what it is and understand that all the election commentary just doesn't mean very much for your investment portfolio.