Mobilizing your base so more of them show up to the polls seems to be a good way to win elections.
2016 had low voter turnout.
Dems want to run an 'anyone but Trump' campaign and get an acceptable candidate for their donor class. Rank and file dem voters will fall in party line. I'm not convinced that will work just as it failed in 2016 but it's been the familiar game played for as long as I can remember with a couple of exceptions.
Sanders would be one of those exceptions, IMO. He'll get no traction with the wealthy and Hillary supporters. Question is will he have a deep enough bench of support to overcome those wealthy and Hillary Dems?