Bush was never a conservative and the root of the 2008 debacle is traced all the way back to the 70's and Carter; you can look it up.
Republicans in the US are generally identified as Conservatives while Democrats are generally identified as Liberals.... thus Bush was Republican / Conservative.
Republicans like to be more conservative towards things like spending money on its citizens, restricting freedom on personal choice such as same sex marriages & abortions, they usually base most of their principles on religious dogma, etc.
Democrats are generally viewed as the opposite where they're more liberal towards personal freedoms like the mentioned above, they generally like to spend more money on the public, etc.
And hell, if you want to try and trace the fault as far back as possible, why not place the blame on the chimp that evolved into the first human?
Maybe that's a bit too drastic.... how about blaming it all on the Great Depression?