Corbyn seems to have done a fine enough job smearing himself over his long and illustrious career of far-left populism and terrorism apologia. His campaign signed up a lot of fly-by-night party members and was successful in getting him elected party leader, but convincing the general public was far more difficult.

(Part of the answer to why Labour has been out of power for 13 years is the Corbyn disaster, it explains half of that time span).