Wasn't just Clyburn. Obama organized for all the candidates besides Biden and Warren to drop out ahead of SC. This was to ensure that the centerists didn't siphon votes from Biden but Warren did siphon votes from Bernie.

Also Biden didn't have the organization to do well on super tuesday because the establishment didn't like him until they decided he was their only choice for stopping Bernie, so his campaign was anemic and underfunded. They solved this by having the democratic committeemen step in as an impromptu campaign organization where Biden didn't otherwise have get out the vote operations. So they had the democratic party whipping up votes for a particular candidate in their own primary election.