It isn’t easy to earn interest income these days. Interest rates on government T-bills, banks’ savings accounts, and certificates of deposit are microscopic. You can blame our government and central bank. They have “ZIRPed” millions of American savers. Here are the details: According to the U.S. Treasury Department, the average interest rate paid on federal debt, as of July, was just under 2.4 percent, implying an annual interest expense on $14.5 trillion of debt of nearly $350 billion. (Net debt, subtracting intra-governmental debt is lower; actual debt, including off-budget items, is higher.) If the average interest rate rose to 5...