This doesn't strike me as credibly accused. Marvelously vague 35-year-old accusation with (so far) no corroborating evidence that was deliberately withheld during the initial hearing.
That's fine, but most impartial people find it credible as you can see if you look at the news or the reaction of public officials from both parties. (non partisan sites only) Credible does not mean true, it means worth taking seriously. It's an accusation from a highly regarded individual that has been known by impartial third parties over the course of at least 6 years, including when Kavanaugh was not up for this nomination. That's credible enough to be taken seriously and it's why even Republican senators have been breaking ranks to stall the nomination.