Bernie IS the progressive favorite. Period. Of the others who may run, Tulsi Gabbard is certainly progressive, but the others?
Elizabeth Warren, I suppose. Kamala Harris? Joe Biden? Cory Booker? Beto O’Rourke? 
Get outta here!
Never let your morals stop you from doing the right thing.--Isaac Asimov
The United States is also a one-party state but, with typical American extravagance, they have two of them.--Julius Nyerere