The Federal Reserve’s Open Market Committee is moving closer to beginning what is likely to be a long and drawn-out process to gradually and predictably unwind the U.S. central bank’s huge portfolio of agency MBS and debt – the sooner, the better, according to Fed chief Janet Yellen. “The FOMC intends to gradually reduce the Federal Reserve’s securities holdings by decreasing its reinvestment of the principal payments it receives from the securities held in the System Open Market Account,” she said this week in her semi-annual Humphrey-Hawkins testimony on monetary policy to members of Congress. “Specifically, such payments will be reinvested...