The question is, why did he first lie and then quietly file an affidavit admitting the truth?
The obvious answer is that he figured that the truth was bound to come out eventually, so it was better if he broached it than somebody else. But then why did he lie in the first place?
The obvious answer is that it’s a lot harder to fire a black Democrat senator from his job than it is to refuse to appoint him. He obviously figured that once he had been appointed and confirmed by the Senate, then he was golden, and there was no chance, realistically, that the Democrats who control the Senate would boot him out.
What, a bunch of white Democrats boot out a black senator? I think not.
Remember, they didn’t want him in the Senate to begin with.