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.
The market tanked because of the financial crisis and because of Obama. Part of the reason the market started plunging in October 2008 was because investors began to anticipate the very real possibility that Obama could win the election, and started selling ahead of the election. The financial crisis combined with Obama caused a brutal selloff in the fall of 2008.
Just checked my chart history: The S&P 500 index closed October 2008 at 968.75. Then after the election it plunged to a new low of 741.02 in November. So the market's collapse started before the election and then got worse after the election. The energy sector tanked much more than the overall market after the election because of fears (large unfounded) that Obama would tax the energy sector much more heavily.