Today’s Wall Street Journal carries the amazing story of a small Texas brokerage that pulled a fast one on some of the biggest banks in the world. The short version goes like this. Amherst, the Texas brokerage, and others sold hundreds of millions of dollars of credit default swaps on bonds back by $29 million of subprime mortgages to JP Morgan, Goldman, UBS RBS and other banking giants. The banks paid steeply for the swaps—up to 90 cents for every dollar of insurance—but thought it was easy money. After all, these were Lehman packaged California subprime loans made in 2005,...