Why? Mr. Fisher argued that megabanks not only threaten taxpayers with bailouts, but that their continuing failure to lend is also thwarting the Fed’s efforts to jump-start the economy by keeping interest rates low. “I submit that these institutions, as a result of their privileged status, exact an unfair tax upon the American people,” he told his audience. “Moreover, they interfere with the transmission of monetary policy and inhibit the advancement of our nation’s economic prosperity.”

Smaller institutions, by contrast, have continued to lend in the post-crisis years, especially to the kinds of modest-size businesses that create so many jobs across the country. According to figures compiled by Mr. Fisher’s colleagues at the Dallas Fed, community banks — defined as those with no more than $10 billion in assets — hold less than one-fifth of the nation’s banking assets. Nevertheless, they hold more than half of the industry’s small-business loans.

Huge banks must be restructured and their access to the safety net scaled back, Mr. Fisher said, because neither regulators nor market participants have proved effective in monitoring risks at these institutions.