While the industry continues to debate the merits of allowing Fannie Mae and Freddie Mac to build a capital cushion for “zero day” in 2018, investors in MBS have a different agenda: making sure that whatever the future holds for the government-sponsored enterprises, it had better include a federal guarantee on conventional mortgage securities. Without it, the MBS market would suffer greatly – as would residential lending and the sale of new and existing homes. So far, no one knows...