Certainly, no unshriven transgressor could criticize others for committing the same transgression, regardless of time passed. One would also have to do nothing to cover up the act, or pressure others to do so. Most important, one should come clean at the first meaningful opportunity. An FBI background check is probably as good a time as any. Because we can't go on choosing leaders this way, not if we don't want voters to become ever more disaffected.
Life is more complicated than that, and politics ought to be, too.
Let's play a game. Let's say Anita Hill told the truth. Clarence Thomas admits to having been a pig in the early 1980s, before society had made clear its taboo on such behavior. He expresses sincere regret, reminds us that he never laid a hand on her, helped rather than hurt her career and had truly not understood how his actions made her feel. Patricia Ireland shakes his hand, accepts his apology on behalf of women everywhere and refocuses the debate on his judicial opinions and writings.