That being said, I believe that he never gave up on his pacifist beliefs (in line with the authors). His Ethics is full of it—but it is also full of the nature of what it means to live in a fallen world and take on that fallenness in a redemptive way.
In the end, I think Nation, et al., are wrong about Bonhoeffer's involvement, but correct that he never gave up on pacifism and God's power. A paradox, indeed. And who isn't full of paradoxes? I think the way out of this paradox is Just Peacemaking. It certainly helped me in my stand on pacifism. Only now I would call it nonresistance, based on my reading of Love and Nonresistance a few years back.
Long way around to say that Bonhoeffer, for all his faults and frailties, was a follower of Christ, doing what he thought was faithful to Christ in a difficult world. Would that we were half as faithful...