"Why use Obama last 3 years?" Easy. Because the first 5 years were spent   

"Why use Obama last 3 years?"

Easy. Because Obama's first 5 years were spent recovering from the Great Recession.

'W' didn't 'cause' that crash but he made that recession inevitable with his detabilizing policies, such as the 'American Dream Downpayment Act', which removed all home speculator's risk. From that point on, the mantra was buying a house at any price was foolproof, you could always sell it for more than you paid. Que the Black Tuesday Wall Street crash analogy: and there it is. 'W' initiated an effective action to right the economy but Obama continued it. The success of that policy wasn't assured, there was great economic and polityical risk incolved.