Remember that in the primary, Biden was saved by the Democratic establishment rushing to stack the deck in his favor in late February/early March.
Lol he was going to win SC with or without an endorsement. That win would have propelled him to victory regardless because the majority of Democrats did not think that Bernie was electable
That was also an effect of Biden being relentlessly promoted by the mainstream media after SC. If Buttigieg & Klobuchar had remained in the race until on or after Super Tuesday, Biden would likely not have taken the lead he actually did, and the narrative following that might have been Sanders in the driver's seat instead of Biden.