Short answer: Surprise! The Democrats.
I've written here before about one or more very quiet initiatives during the Clinton Administration that were undertaken by the White House to beef up Democrat-friendly voter roles, particularly in California, by rapidly processing Hispanic immigrants into citizenship and, en route, registering them as Democrats. Illegal activities abounded here, but of course were never reported because the media, all socialists, had no interest in letting people know about the demographic bomb that was happening. I've discussed this in HaZzZmat before, and will follow up at some future point when I have time to look up the links to back this up. Suffice to say, the state that gave us Ronald Reagan and predictable conservative electors (53 of 'em) for many years is now overwhelmed with new Democrats who've taken the state pretty much permanently out of the GOP column.
Fast forward just a bit. Another swell way to make sure new immigrants stay in your party's pocket is to give them really nice goodies. In the Second Clinton Administration, the Clintonistas put pressure on Fannie Mae and Freddie Mac--those "quasi governmental" creations so much in the news of late and creatures of the Roosevelt and Johnson administrations BTW--to buy essentially substandard mortgages that they normally wouldn't buy because they weren't safe. This had the effect of bringing rates down for individuals with less money to purchase homes. I.e., the new immigrants the Dems were assiduously courting in order to eventually strip southwestern states off forever from the Republicans.
This, too, was a success. And it snowballed in the early 2000s, as Clinton left the White House--remember, Bush didn't occupy it until 2001--as Fannie and Freddie pressured banks and other institutions to originate these bad loans. The lending institutions for their part, after some initial skepticism, were happy to join the party as the spreads involved in substandard loans made them rich beyond avarice. The ultimate result is the current disaster.
Lest you imagine that Bush and the Repubs were asleep at the switch and ignoring the increasing danger of the enormous number of risky loans, don't forget (although the media wants you to) that Bush and the Repubs tried to ram through a 2005 bill to get this mess under control. The Dems ganged up and rejected it. Fun fact: the bill's co-sponsor was John McCain.
And while we're at it, the two Clintonistas who ran Fannie Mae while this mess was being cooked up--Jim Johnson and Frank Raines--profited handsomely from it before their outrageous behavior caused their eventual ouster. They are now Barack Obama's fiscal advisors.
More to come.