@engineer,
I believe that is a very accurate assessment of the situation.
Sanders had the committed support of about 24% of the Democrat electorate in the 2016 Primary, and they appear to be sticking with him, though there appears to be little prospect for decisive growth. My impression is that the Democrat leadership is aware of the likely ineluctability of the ascendant new left among them (Warren included), and that is their likely motive in supporting Joe Biden. Unfortunately for them ol'e Joe is amply living up to his career-long record of gaffes and venality. The only thing left for them is impeachment, however long it may take and whatever may be the short term cost. They will thus continue to pursue it in the face of declining likelihood of success.