The turnover at the top of the Securities and Exchange Commission comes as the agency copes with challenges ranging from high-frequency trading and the regulation of the money market industry to the writing of many of the rules required by the Dodd-Frank Act. A Reuters story notes that another challenge is figuring out who will run the SEC over the long run. President Obama named SEC Commissioner Elisse Walter to replace the outgoing chairman, Mary Schapiro, but is expected to nominate a permanent successor before Walter's term expires at the end of 2013. While Walter serves as chair, the commission will have two GOP voters and two Democratic voters, a split that could make it harder to pass key measures, Reuters notes.

The Wall Street Journal argues that Schapiro's departure leaves a “regulatory void” and that major issues like the Volcker rule may have to wait until a permanent chairman is in place. Possible nominees include Mary John Miller of the Treasury, Sallie Krawcheck, formerly of Bank of America, and Finra Chairman Robert Ketchum. And it suggests that some key SEC officials appointed by Schapiro may exit in her wake, including enforcement chief Robert Khuzami.

MarketWatch offers Walter a to-do list, suggesting that she use more sophisticated methods to monitor computerized trading, coordinate better with the Commodity Futures Trading Commission, support Robert Khuzami and the enforcement team, and try to slow the revolving door between the SEC and securities firms.