(CNBC) As the only self-described democratic socialist in the U.S. Senate and the Democratic presidential race Bernie Sanders represents a unique figure in American political life. Four years ago his message of dramatic change to remedy income inequality and other economic ills won a large following in his fight against Hillary Clinton for the nomination of a party he does not even formally embrace. The results encouraged him enough to try again for 2020 even at age 78. This race poses different and perhaps more formidable challenges. The political independent faces not only a moderate conventional front-runner in former Vice President Joe Biden but also a powerful fellow liberal in Sen. Elizabeth Warren brandishing ideas nearly as ambitious as his. In debates and on the campaign trail Warren has expanded her support this year; polls suggest Sanders has not.