"A Mighty Fortress" Has Grim Reality
I personally think A Distant Thunder is the best of the three novels as far as just being a damned good, ripping and gripping read goes, but I can see how A Mighty Fortress would give our Movement Nervous Nellies the jim-jams.
There's a certain grim reality in AMF that is kind of absent in the others. I think Bobby Bells and Nightshade have a lot to do with it. They're people you can actually imagine existing, and that speech of Chelsea Clinton's with everybody sitting around watching it in the safe house is something you can see happening in your mind. Yeah, the impression you get from AMF is "My God, this guy means it." And that of course causes Movement wimps to brown their briefs.