Fannie and Freddie paper was not backed by the government. It said so in the prospectus. But even Jim Jubak, one of the more reasonable talking heads, was howling how the government had to make all that paper good, or, supposedly, no-one would buy Treasuries, which are explicitly backed by the government.
Guess it all depends on who would take a haircut, vs who would benefit, from a particular insolvency?
Steve