Also
Foreign governments ASSUMED that Fannie and Freddie had the FULL FAITH AND CREDIT of the US government.
That is why foreign governments purchased so much of our mortgage debt.
The Democrats who ran and controlled Fannie and Freddie did nothing to discourage foreign investors, on this point.
On the whole, US and foreign institutional investors, not foreign governments, purchased US mortgage backed CDOs. Insurance from AIG was required because it guaranteed a steady income flow and the value of the CDO, something that even the implicit US government guarantees of Fannie and Freddie mortgages could not assure.