Did Fannie Cause the Disaster?

In a word, no.  Those who are saying it did can be put in the collection of folks that have a casual relationship with the truth.

Along with many other experts, the nine members pointed to considerable
evidence that, despite large losses, these government-sponsored
enterprises (GSEs), as they are known, bought or guaranteed too few
highly risky loans, and did so too late in the 2000s, to cause the
crisis.