The media narrative was **extremely terrible** for Biden when he came back to win South Carolina by 30 points after having been tied in the polls days earlier.
That SC win created a lot of momentum/favorable media heading into Super Tuesday, and Super Tuesday created further momentum. But Biden really earned that SC landslide by having the trust of black voters and non-college whites who are key in SC (+ Clyburn's endorsement).
Only two candidates (Biden and Bernie) ever really had a mutli-racial, multi-class coalition, which is usually how win the D primary. Of those 2, only Biden really built bridges to the rest of the party, which is usually how you win *any* party nomination, Trump an exception.
On top of that (and this is related to his running as a somewhat generic, coalition-building Democrat) Biden's policy preferences were probably *closer* to those of the median Democratic voter than any other candidate. (Though not the median Democrat on Twitter.)
Did "electability" help Biden? Probably. I think it *hurt* all the candidates who weren't straight white men. But at least Biden demonstrated his case by having higher turnout in his stronger areas. And overall the media narrative was skeptical of Biden, especially post-IA/NH/NV.
