Elizabeth Warren’s admirers often refer to her as a grandmother from Oklahoma. This is technically true. It’s also what you might call posturing. Warren, 62, is a Harvard professor and perhaps the country’s top expert on bankruptcy law. Over the past four years she has managed to stoke a fervent debate over the government’s role in protecting American consumers from what she sees as the predatory practices of financial institutions, and she has positioned herself as the person to oversee a new federal agency to rewrite the rules of lending. Warren is a grandma from Oklahoma in roughly the same way Ralph Nader is a pensioner with a thing about cars.