A mixture of greed, idealism, cynicism and stupidity led to the practice of bundling those iffy mortgages into financial instruments that Wall Street didn't know how to handle and regulators didn't know how to regulate. As Rep. Barney Frank (D-Mass.) put it in 2003, he wanted to "to roll the dice a bit" on regulating subprime mortgages.
When the Washington-abetted housing boom went bust, regulators demanded immediate markdowns of mortgage-backed securities, which required financial institutions to sell them, creating a fire-sale atmosphere that fueled the panic even more. The Federal Reserve responded by letting money tighten in a way it hadn't since the 1930s.
Some Obama defenders will say that Bush's deficits made it harder to deal with the crisis. That seems reasonable, even if it's a red herring in the debate about what caused the crisis. And Obama's record on deficits hardly gives him much standing.
I once thought that Obama's relentless Bush-blaming was simply a mix of political expediency and gracelessness. But the truth is more complicated. Liberals have smartly, albeit cynically, laid the case that Bush was Herbert Hoover in order to make the claim that Obama is Franklin D. Roosevelt. For this to work, Hoover must be remembered as a do-nothing free-market guy. But Hoover was no such thing. He nearly tripled government spending in response to the Depression. FDR used Hoover's spending as a baseline for his own, even as he dishonestly decried Hoover's passivity.
Obama has done largely the same thing. The first bailouts of the crisis were supported by Obama but launched by Bush. The same goes for the first stimulus. Obama simply tripled down on all that while claiming he was breaking with Bush.
Or maybe I have that all wrong. Maybe we could get some clarity by asking the president, "What are you talking about?"