When Neil MacBride, U.S. attorney for the Eastern District of Virginia, told The Wall Street Journal in May that he was putting together a new “investigative taskforce” to crack down on financial crime and securities fraud, the news didn’t strike many as a significant development.

After all, most federal prosecutors’ offices have various taskforces or units set up to focus on specialized areas. Moreover, MacBride’s jurisdiction in Virginia is hardly a hotbed for financial fraud. MacBride indicated, however, that his ambitions extended well beyond the borders of Virginia. His bold claim: “I think Virginia ...