I've heard the claim 'this accusation is credible'. Let's forget about this specific event, because that isn't my point. What would a non-credible accusation look like? Just wondering if this is a throw away comment, or we actually have a definition we are following here.
There are real definitions, but they are irrelevant to political cases where people are just signaling red/blue affiliation. In a non-politicized context: specificity, character, corroborative witnesses, circumstantial evidence, etc.