Surely Brau-1589 killed Roosevelt because Atom told him to do so? I mean, I can't think of what else Atom would have wanted him to do, when he visited. I'm amused at how Brau-1589 was able to get there so easily, though.
While I would have liked more closure regarding 'Thracia' and the general political aftermath as well, I don't think the ending was *that* open-ended or unsatisfying.