First off, for this sort of issue, Wikipedia is not a sufficient citation.
Secondly there are multiple types of sub-prime mortgages. The definition of sub-prime is someone who has less than Good+ credit. The historic rate of default on this for CONFORMING loans is very low.
The problematic sub-prime mtgs were the ones that allowed more than 80% LTV, had 3 or 5 year "rate resets" and similar mechanisms where the actual mortgage itself was one in which the borrowers lacked sufficient cashflow to service the loan outside the initial introductory "teaser" period.
The CRA, nor Fannie Mae/Freddie were permitted to issue or acquire such loans prior to 1998/9. Prior to the deregulation of the mortgage industry, such loans DID exist but they were rare and were typically held and serviced by the specialized lenders that created such mtgs (HFC aka Beneficial, and special subsidiaries of Countrywide etc).
So the "sub-prime" loans in question with Fannie and Freddie were not the problem. Its not even given that we had a real "housing bubble". Its true that house prices started to exceed the ability of average income individuals to service the debt in 30 years, but that was more due to stagnation in the middle class wage than in any housing bubble. Construction costs currently are around $100/sq ft for average construction. That means a 2,000 sq ft house (not very big) costs $200,000 not counting the land. At the historic avg mtg rate of 6% and 20% down, that's around $1200/mo in payments. The gotcha is that the average income family with no other debts can theoretically afford $980/mo.
But that's necessarily a "bubble" because 10 years earlier, that same median income COULD afford exactly that house. The gotcha is that median incomes stagnated. Now if hat family is willing to foregoe some other expenses, they CAN afford that $1200. And that is what the change in Fannie lending allowed.
But what happened after banking dergulation in the late 1990s was that Solomon and others were allowed into the market. And they saw how lucrative the "hard money" part of the sector was (where HFC were playing). AND they were motivated by a huge influx of invesment cash from the booming APAC economies.
So they started rewarding banks and other lending organizations for packaging together CDOs without askeing the hard questions that HFC et al used to ask ( used a "hard money" loan in the early 1990s because of medical bills, and a deregulated "sub-prime" in 2002 as funding for a smalll business - paid off both). This resulted in a huge number of problematic loans: 100+% LTV, 3 and 5 year resets, Interest only, NINJA and Liar loans etc. These were packaged up and sold alongside the Fannie and Freddie "sub-primes" as equivilent.
But they were not equivilent. And as the 3 and 5 year resets kicked in, they caused a collapse of the CDO market. At which point Gresham's Law (that's what wikipedia is acceptable for as a reference, definitions), kicked in and essentially caused ALL SIVs (structured investment vehicles) to be valuated the same as the bad ones. This in turn caused some institutions to fail and others to simply lock up on short term lending.
Why lock up short term lending? Because banks are required to carry loan reserves. They typically carry this in "safe" interest bearing investments that can readily be converted to cash. Things like SIVs and other bond type vehicles. Except that as the SIVs have ceased to have a liquid market into which they can be sold, they cease to be able to be considered "loan reserves". Since the banks cannot call in their long term loans (mortgages) they can only make their reserves work by STOPPING LENDING on short term loans.
That means that Joe's Machine shop with 6 employees cannot get an Account's receivable loan to make its payroll with. So Joe's Machine has to lay off its employees. Who then cannot make their FANNIE mortgage payments, which then causes Fannie to get into trouble.
- IF the problem had been caused by the 1994/1996 relaxations on Fannie and Freddie, you would have seen the market die in 1999/2000. Yet that is when these problem mortgages only STARTED to boom.
- IF the problem had been caused by Fannie and Freddie, then bailing them out OVER A MONTH AGO would have fixed the problem.
NEITHER occured.
QED the problem was not caused by Fannie or Freddie or their 'sub-prime' mortgages.
The problem was caused by deregulation of banks and investment banks. This deregulation was a policy of, was pushed through by, and then subsequently mismanaged even worse by The GOP Congress and the GOP Bush adminstration.