You could call it "dredged up", or you could call it a letter from a civil rights leader vigorously opposing his appointment as a judge that would still have relevance to him being appointed as AG.

As for regret, I haven't seen anything about Coretta Scott King changing her opinion, and if you're talking about whoever found that letter and spread it around, I don't see how that would be relevant. I don't know where you're getting this info.