President Barack Obama is to call Thursday for limits on the size and complexity of large financial institutions. He will make his pitch standing between former Fed chair Paul Volcker and the Bush-appointed former SEC chair William Donaldson. Obama will endorse Volcker's proposal for restricting proprietary trading done by commercial banks. On Wednesday night, Treasury Secretary Timothy Geithner had a private dinner with Wall Street executives. Observers say that the emphasis on banking regulation is an attempt by the White House to win back some of the populist fervor which helped Republican Scott Brown win Tuesday's special election in Massachusetts.