The ecomomy was ruined by the banks and mortgage companies who were making high-risk loans, and by the idiots (who were not quite as wealthy as they thought they were) who took out those loans. The mortgage industry collapse then caused a domino effect that dragged the rest of the economy down behind it.
There's a lot of blame to go around. Anybody who says it was Bush (it wasn't), or "rich greedy people / really wealthy people" (it goes well beyond that) that caused the crash isn't looking at the entire picture. Blaming the rich/wealthy for the crash is just buying into the Obama class warfare rhetoric.
I don't think there's a huge swing of voters in the last couple of elections, nor in the upcoming one. There's a large base that will always vote for the Democratic nominee no matter what, there's a large base that will always vote for the Republican nominee no matter what, and there's the 10% or so in the middle that actually decide the election. You know which groups/demographics largely make up the Democratic base, and which groups/demographics largely make up the Republican base. None of them are going to budge from their party nominee.