In 2008, probably a lot (they thought he would fix the economy and bring back opportunity); in 2012, not so much (many). Unfortunately they didn’t show up for his opponent either; he was too rich and too white and too male.
The amount of voter apathy I’ve seen for decades is creepy; ignorant people just assume they have no control over anything and just bitch & moan without voting. Many people (anyone who didn’t vote against him) deserve Obama.
Truth be told, the 2008 economy was more than just Bush at the helm, like most collapses it was a culmination of too many people mishandling their money or just too many people with too much debt having their loans called in, yet they were unable to pay. Throw in student debt, a mess was inevitable.