Sen. Elizabeth Warren, the founder of the Consumer Financial Protection Bureau and the scourge of big banks, is often mentioned as a possible running mate for Clinton. Warren excites the progressive wing of the party, which could be crucial as those Democrats have largely supported Bernie Sanders' rival bid for the presidency. Still, there are reasons why a Clinton-Warren ticket may be unlikely. For one, Warren hasn't endorsed Clinton, which is something of a prerequisite. For another, Clinton hasn't been willing to go as far as Warren in a number of areas, including with regard to financial services policy. In short, Warren may be too liberal for Clinton.