That is true, but keep in mind that the S&P 500 index plunged in November 2008 mainly because Obama was elected. I saw that plunge in real-time and it was absolutely incredible how badly the energy sector was decimated in that selloff. So Obama started with a badly beaten-down market that sold off hard because he was elected. Then the market got worse as the economy tanked badly in December 2008 and early in 2009.
The crash in 2008 was caused way before Obama got elected. By the time of the election there was a very real possibility that the US economy would completely crash bringing the entire global economy crashing down.
The S&P had already crashed from above $1500 in December 2007 to below t$850 in October 2008.