He resigned his commission otherwise he couldn't speak out. Once a Marine always a Marine I don't think he will be silent or take any crap from those who try
That might be his intention. When they hit 0-5 (Lt. Col) they know if they are going to make Colonel (O-6) or not and most hit 0-5's are not too far from retirement, around 20 year mark, unless they are 'fast tracked' - meaning - they are exceptional and/or have caught someone higher up eye for whatever reason then they can make Colonel much early which also usually ensures they have a good chance of making their first star (Brigadier General) unless they screw up. Also, with the war(s) over, promotions will slow down a lot and be harder to achieve so... So, my guess, is he knew what he was doing and how this would play out - yet - felt he had to speak out and so he did. Hell, he probably already had his mind made up to take retirement and decided to go out with a bang, not go quietly. We need more like him in the military and in our government...