By the time the U.S. Treasury responds to the Federal Housing Finance Agency’s request for additional capital to keep Fannie Mae and Freddie Mac afloat, the GSEs will have absorbed $150.2 billion from the U.S. taxpayer to help cover the massive losses the companies have suffered in the collapse of the mortgage and credit markets. But now the biggest hurdle Fannie and Freddie may face in a return to positive earnings is...