Warren's a problem. By various standards, she's not that extreme. Although she's more extreme than Obama, Warren's in the range of Hillary. Bernie is about as extreme as you'll find in Washington. See the On the issues comparison:
https://fivethirtyeight.com/features/how-elizabeth-warren-could-win-the-2020-democratic-primary/.
But Warren is unique in the Democratic party and frankly in Washington in those disliking her. Of many coming back to congress, Fivethirtyeight called her the 'weakest incumbent' based on her 2018 results...this coming from arguably the most liberal state in the country. Even worse, she is stunningly liked less than Donald Trump - the least popular president since measurement began.
Warren needs to be contested soon. If she remains the spokesperson for the party, that will be a blow.