correction: Yes, he is a reputable commentator. But his unpublished essays are not reliable sources in the sense that his academic publications are. Second, he's is this field a general political commentator, not an academic, and makes no pretense and being unbiased. Of course, everyone who writes on this subject is probably biased somewhat. Perhaps we can quote him after all, if we make it clear it's an essay. But I'd still hope for better sources.   Incidentally, if anyone is interested, I  think his Wikipedia bio  needs some work in the direction of objectivity, and rewriting the parts copied directly from his web site.