Dr. Thomas Sowell (PhD – Economics, Harvard) has an excellent column on the roots of the financial mess and its impact on the campaigns.
The New York Times has an article here from a few years back on regulation that (obviously) ought to have been done. And McCain was involved in responding to the forecasted failure of Fannie and Freddie in 2006 here.
Two Wall Street Journal videos (here and here) present the history of the mess through investigation by the WSJ of the history of the issue and through the words of members of Congress. There also is a YouTube video getting wide circulation in which members of Congress explain the issues in their words.
It’s normally quite difficult to be able to summarize large issues in only a few lines, but reviewing the above will allow just that in this instance.