I would speculate Republicans are wildly happier when "their team is 'winning'" and Democrats would have a boost in happiness with Democrats in power, but nowhere near the swing of Republicans. Democrats, IMO, are more aware of the *real* current and longterm problems the US faces while Republicans listen to whatever Republicans say the "problems" are - "problems" that are too often very outlandish and not based in reality.
I agree that both probably swing depending on who’ “winning”, although I bet that generally the Dems tend to be significantly less happy and therefore swing less, relatively.