@Olivier5,
From where you get this idea, not to mention to hold it with certainty, I do not know. It makes no sense electorally. It makes no sense organizationally.
I gather you are presuming that the gravitational pull of big corporate money will inexorably draw any Dem administration to the right. No question that force will be in play as it always is. But assuming that a Sanders administration would have the actual, real world capacity to
successfully fend off this force better than a Biden administration (as it will be constructed now) strikes me as naive.
Further, though the presidency is very important, what is also critical now is advances down ballot at the state level. Dems made a LOT of progress here in the midterms because of passionate Dem voter turnout - which is perhaps the most salient aspect of this primary season. Biden is not damaging that trend at all, he's improving it.
And in any case, what the Dem party will do ought to be, for the most part, established by a consensus of Dem voters. The left must do a better job of making their case.