Falling interest rates tripped up Fannie Mae and Freddie Mac during the fourth quarter, indirectly leading to sharp declines in profitability despite continuing gains in their key mortgage-backed securities guaranty fee operations. Together, the two government-sponsored enterprises earned $1.54 billion in net income during the fourth quarter of 2014, down 74.3 percent from the previous quarter. With their retained portfolios in shrinkage mode, net interest income was down 11.9 percent from 2013. The big factor was...