Presidential elections in the United States are held for every four years. The vast majority of investors and popular press personas believe that this occasion is likely to affect the stock's market fluctuation. Many academic papers are also indicated that shifts in political party could influence the stock market and change the outcomes for investors’ portfolios. History shows an interesting pattern in which election's cycles are correlated to stocks' market returns, both negatively and positively. This paper discussing about how, rottenly, the stock market is reacting both before and after elections, and it is aiming to observe the impactful forces of the presidential elections on the capital market and other financial markets. Additionally, this paper will analyze the Capital Asset Pricing Model (CAPM), and, hopefully, would supply useful insights for future investment decisions.