Brian Downey is having some fun with the Sumner-Johnston-Mac-Davis post, wondering if my synopsis suggests that Edwin V. Sumner was a knucklehead or a Queeg. If Brian is wondering, certainly other readers are too.
This gives me an opening to return to the content of a very worthwhile study.
The Delafield Commission and the American Military Profession, on which the post was based, stresses repeatedly that Johnston and McClellan were obsessing not about Sumner's intelligence (despite the sharp quotes from JJ) but rather about his theoretical faculties and the potential for what we now call cavalry doctrine. (This is a bit of anachronism - in that day JJ and GBM could only get to the modern concept "doctrine" by referring to a combination of "regulations" plus "method" or "system.")
The fear of Sumner seems to boil down to this 1856 comment from JJ to GBM: "The old infantry notion exists here [in the First U.S. Cavalry Regiment] - that to make a decent appearance on dress parade - is the only object of instruction. [...] Our men have not been taught to use their arms & their best instruction in riding has been in watering their horses." He told McClellan (quite reasonably I think) "Our only chance of reform is in the influence you may have." He says also, "My hopes of U.S. Cavalry are in your efforts - so bestir yourself." In another message he alluded to the need to "compel" commanding officers [Sumner] to attend to the training of the horsemen.
McClellan had indeed bestirred himself - he translated Russian army regulations and a Russian cavalry manual for the U.S. Cavalry. He had additional European cavalry analysis from his European tour. However he and Johnston split on how to manage the matter.
Author Matthew Moten says that Johnston urged McClellan to submit his materials directly to Davis, appealing to Davis's expertise (and vanity?) as an old cavalry commander. Johnston's approach was to get a fiat, an ukase from the SecWar.
McClellan, on the other hand, whether from humility or insecurity, got stuck on the idea of forming an Army Cavalry Board to review and ratify his materials. He opened a correspondence with Davis on the matter. Moten imputes to GBM the aim of making Johnston head of that board. But Johnston warned Mac that such a board, if created, would be stocked with dragoon officers - a very bad turn for a cav doctrine.
Johnston seems to have had a good read on Jeff Davis. Davis rejected the idea of a board - it would be too slow in getting cavalry doctrine off and running. He wanted to see McClellan immediately - and the Russian materials too.
But in fact Davis split the difference on cavalry boards by urging McClellan to consult with the likes of William Hardee, then superintendent of West Point. He wanted Hardee to furnish McClellan with resources for doctrinal cavalry trials at the Military Academy. McClellan balked at the notion of submitting cavalry regulations to such an infantry-minded officer and he made the classic junior officer error of baldly explaining to Davis his objections to cooperating with Hardee, an argument that contested Davis's preferred route forward.
Moten believes in this letter GBM offended Davis. He was summoned for a meeting with Davis and "There is no record of their discussion." A few days later, GBM resigned his commission, delaying its effective date until his Delafield tour report was completed.
Whichever way the cards might have fallen in this matter, it seems Sumner would have been excluded from a ratification of the new doctrines, whether by Johnston's hopes, McClellan's board, or Davis's inclinations. Not because he was stupid, but because he was an old soldier set in his ways.