Shortly after being nominated by President-elect Donald Trump to be his Treasury secretary, investment banker Steve Mnuchin midweek dropped a bombshell on the mortgage market: Ending the conservatorships of Fannie Mae and Freddie Mac would be a top priority. For the most part, the mortgage industry cheered the news, believing that at the very least, Mnuchin would preserve the federal guaranty on existing MBS and into the future. In fact, the market seems to be betting on it. But now comes...