But then the guy seems to have left of his own accord, rather than being fired.
I'd say its pretty hard to consider ANYTHING about this guy GOP. At all. If he was a Republican staffer, I'm VERY sure he didn't let anyone know how he really felt. If he had, he would have probably been fired a long time ago. I'm actually surprised he didn't leave his job sooner, if he hates the party as much as it seems he does.
For the record, the guy's worked as a staffer on Capitol Hill since at least the early eighties. It's entirely possible he watched the party change around him but kept quiet and because he didn't want to lose his job and cause his entire family to pay for his own ideological dispute.
Also, for the record, he was a professional staff member for the Senate Budget Committee, with enough seniority to make a six figure income, so it's not like he wasn't in a position to know what was really going on.