Fannie Mae and Freddie Mac could be toast one of these days.
Speaking broadly, Fannie and Freddie are essentially low-volatility versions of LTCM, w/o the exotic conversion trades. They are WILDLY overleveraged, and haven't the first clue as to what to do when their lending pyramid begins collapsing, as it will start to do if interest rates should suddenly rise sharply, more sharply even than the long end of the curve has risen from May to the current date. Maybe the pyramid won't collapse; Greenbean and the boys will do everything in their power to see that it does not.
But, do you or anyone want to bet the entire financial future of the US on that proposition?