Trump is using authorities granted by the 2008 conservatorship of Fannie Mae and Freddie Mac that allows the companies to increase by around $200 billion their holdings of mortgage bonds. (Treasury could in theory modify the preferred stock purchase agreements with the companies to raise existing caps on the firms' investment portfolios to accommodate even larger purchases). Before 2008, Fannie and Freddie could and often did buy investments when it saw attractive opportunities, which could tighten spreads. Since then, the Fed became a larger buyer of MBS during QE programs between 2009-14 and 2020-22, though they didn't do this with a profit motive in mind (and in fact have run up large losses on the Covid-era purchases). What's notable about this intervention is that it's being done during a period of relatively solid economic activity and with no meaningful stresses in credit markets.(Nick Timiraos)