These interesting facts are well known in the academic literature. The latest study, which is forthcoming in the Journal of Political Economy, is freely downloadable from https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2909281. It argues that causality runs in reverse---it is not Democrats causing high stock returns or strong economic growth, or Republicans causing low returns or low growth. Instead, people tend to elect Democrats during crises (think Obama getting elected in November 2008, or FDR in 1932), when stock prices are low and expected future returns are high. And we elect Republicans in good times, when stock prices are high and expected returns are low. This voting pattern delivers high stock market results under Democrats and low returns under Republicans.