I don't know the details, but from what I read on here last night, it looks like he was clerking for a judge (don't know which level) and the judge asked for his deferement.
My interest is mostly curiosity. I guess if a judge asks, the local board complies. As I noted earlier, it's not an issue this election.
As an aside, one of the rare occasions I watch TV rather than read transcripts. He came off pretty well tonight. Admittedly with a friendly interrogator. My guess, he would have eaten Alan up alive.