Economic Scene: Which Party in the White House Means Good Times for Investors?: "The answer is: It's not even close. The stock market does far better under Democrats"

during those 72 years the stock market returned about 11 percent more a year under Democratic presidents and 2 percent more under Republicans - a striking difference.
The return on the smallest 10 percent of traded companies is 21 percent higher during Democratic administrations, while the return on the largest 10 percent is only 7.7 percent greater


causality might go the other way, with market returns driving presidential elections. Perhaps voters feel wealthier when stock prices are high and then vote Republican; when stock prices are low, they vote for Democrats.