Moira Donegan writes in The Guardian:
Like Sanders, Warren has a long career of railing against the injustice of a country where the rich are getting richer and the poor are getting poorer. Unlike him, she has a proven track record outside of the Senate, helping to establish the Consumer Financial Protection Bureau during the Obama administration and writing the book – actually, writing several books – on how to help working families by making finance and debt laws more fair.
This one is important:
The fact is that Warren is to the left of Sanders on some issues, notably gun control.