One of the two unhappy times in AGNC was during the summer of 2011 when the debt-ceiling argument was going on. It was only the birth of the future Fiscal Cliff, and the raising of the ceiling, that calmed AGNC down.
The other was the combination of QE3/4 with the coming of the Fiscal Cliff itself. People who had been buying AGNC in bushels all through 2012 decided they were safer in Zlotys or bordeaux or something. Lots of equity disappeared, taking back a good chunk of the year's gains.
If the new debt-ceiling argument actually does start to threaten the nation's ability to keep the cash flowing, the turmoil will be unfortunate for long-term holders, but a bonus for bottom feeders.