This doesn't answer your question exactly, but I would be surprised if you found any historians' reactions to it at all.

These books generated by political figures (Buchannan; the Killing Lincoln/Reagan/Patton/Jesus books by O'Reilly; the Churchill biography by Boris Johnson)

are not "history" at all. In that the writers do not engage extensively with primary sources and with changing interpretations in secondary sources (i.e. historiography) in any way.

Instead, they have a political agenda (and often a ghostwriter) and their goal is to USE that historical figure or event to push a political agenda. In the process, they cherry-pick a few items and then run roughshod over real honest-to-goodness history... which, if you're a historian, is painful to read. Since we have plenty of great books on our plate already, we usually skip the garbage. :-) There are some dutiful historians who plow through the mess to offer a public 'rebuttal'... but usually there are so many errors in such political hack-work that the rebuttal either is a book-in-itself, or just a few bullet points of the politician's gross ignorance. (It's bit like asking a biologist to review a Creationist account.)

NB: popular history is a very different animal. It's real history, written with an eye to sources and interpretations, but geared towards readability, with all of 'scaffolding' of history hidden. So, Niall Ferguson's Empire--which I personally despise, find grossly misleading and even unethical--is still a solid history. He uses sources and challenges interpretations. I've assigned it in classes (and then demolish it--because it is deeply flawed--and did I mention unethical?), but as a work of history, there is a point to reading it and discussing it. Even Ferguson can give me new historical insight. (and Empire did.) But I would a priori not bother with anything by Buchanan: there won't be anything but opinion there.

So, sorry that this doesn't answer your question, but I hope it might be useful anyway!

Question: what is a paleo conservative?

From what I can tell, it hasn't. The only semi-scholarly looking journal it was reviewed in is something called Samaritan Review. Very broadly speaking, because this is definitely not universally true, academic journals tend not to bother with trade books (i.e. something Pat Buchanan would write). To put it crudely, it sounds like Buchanan has taken Niall Ferguson's The Pity of War, extended it to WW2, and blamed Churchill more.