Pershing Square Holdings, one of the largest institutional investors in Fannie Mae and Freddie Mac common stock, is doubling down on its investment in the two mortgage giants. But it’s taking a different tack, buying up junior preferred stock rather than increasing its holdings of common. The change in strategy was mentioned in the firm’s annual report to shareholders and comes at a time when the chances of housing-finance reform look nil for 2018. How much PSH paid for the junior preferred is unknown. According to the annual report, “Our preferred stock represents approximately 21 percent of our total investment in Fannie and Freddie, or about 1 percent of net assets.”