Removing Giancola from office
OK, a lot of people have argued pretty much what Peter is arguing here -- that is, that Pritchart's failure to remove Giancola prior to his little shenanigans with Grosclaude make her, at least indirectly, responsible for his actions in the sense that she knowingly gave someone she suspected of operating under the "old rules" access to power and didn't remove him when he dropped the dime on Bolthole.
There are several parts to this argument, but to be completely honest, I don't believe that any other menu of choices was available to Pritchart.
(1) Giancola came in second -- a distant second, but still second -- in the presidential election.
(2) Under the Havenite constitution (which is not a clone of the U.S. Constitution, despite similarities) the successor to the president in the case of his death or his being rendered incompetent is not the vice president, who doesn't exist, but the secretary of state. While this is an appointive office, it stands second in the succession of executive authority, which is one reason why it requires confirmation by the senate.
(3) In line with the second point above, it was not at all unheard of in pre-People's Republic Havenite history for a secretary of state and a president to have disagreed with one another significantly.
The tradition in the Republic was that the secretary of state's position was automatically offered to the candidate who came in with the second-highest vote total in the presidential election. If there were irreconcilable differences, and the nominee who had lost the election was supposed to politely decline the invitation. Obviously, that frequently -- or at least sometimes -- didn't happen. However, it was clearly established in the unwritten portion of the Havenite constitutional tradition, prior to the emergence of the People's Republic, that the president's authority was paramount within the executive branch. That is, a secretary of state might disagree with the policy established by the president, but that did not relieve him of the responsibility to do his very best to execute that policy. And if he simply could not agree with that, then it was time for him to leave the cabinet, and, yes, under the original Havenite constitution, the president did have the authority to dismiss him at any time. It was never an easy chore, however, given his place in the presidential succession. No one in the senate could prevent the president from dismissing him (under the original constitution), but they could certainly make the president and his administration pay a significant price if they thought the president had acted solely to remove a political rival from the presidential succession. For example, they could stonewall all of his other appointments which required congressional approval, or they could block critical legislation, or they could basically tell him who they wanted to see nominated for the secretary of state's position and make it clear to him that they had no intention of approving anyone else.
As a general rule, no one was particularly interested in provoking a showdown between the executive and congress, far less a constitutional crisis, but the potential for messy domestic politics was always bound up within this weakness in the Havenite constitution. And, yes, I do most definitely regard it as a weakness -- one which I deliberately designed into the system, since I don't believe in perfect political systems and try my best not to create them in my fiction. The best I think you can expect out of a political system is that it does basically what you want with a fair degree of efficiency, despite weaknesses and problems that have to be worked around. After all, it's designed to govern human beings, who are probably about as cantankerous as any intelligent species is ever likely to prove.
(4) In Giancola's case, Pritchart was looking at several fairly compelling reasons for making him Secretary of State. He'd come in second in the presidential election, which meant he was the logical choice as her successor -- in the view of the electorate, at least -- if something should happen to her. (And don't think that that reflection didn't keep Kevin Usher up at night upon occasion!) He was genuinely popular on Nouveau Paris -- for legitimate reasons, actually -- and had a significant powerbase in congress, which made co-opting him for the administration a reasonable political calculation. As a member of her cabinet, she would be in a better position to keep an eye on him and to sit on him if his machinations (and, remember, she was thinking about domestic machinations) seemed to be getting out of hand. The fact that she didn't share his interpretations where foreign-policy and foreign relations were concerned actually made him valuable to her, in some ways, as an opposing viewpoint within the cabinet which could ensure that questions were looked at from more than one perspective. And, since everyone knew he was her most significant rival for political power, including him in the cabinet -- and, especially, in the post that she offered him -- gave her an "all-parties" administration, which was a very valuable consideration given the fact that she was busy trying to reestablish a civilian, stable representative democracy, which enshrined the rule of law, for the first time in something like a century.
(5) Once Giancola was in the cabinet, and in the presidential succession, getting rid of him would have been a significant problem under any circumstances, and would have required the expenditure of a lot of Pritchart's political capital. Given the inherent instability of the nascent governing structure, the consequences -- both short-term and long-term -- for the Republic could have been significant, even under the best of circumstances. Given the fact that at least one justice of the Havenite supreme court had already given it as his opinion (privately, to be sure) to Giancola that under the special circumstances of this first new administration, the president lacked the legal authority to discharge any member of her cabinet without congressional approval, the stakes rose enormously.
(6) The only thing she knew and could (hypothetically, at least) prove, prior to the outbreak of the new war, was that Giancola had presumably told other members of congress about the existence of Bolthole. Or, at least, that the Navy had something significant up its sleeve in terms of new military hardware. That was it. She had absolutely no reason at that point to suspect he was even contemplating manipulating the diplomatic correspondence. For that matter, at that point, no one in the new government really understood that the secretary of state's control of the diplomatic correspondence would have made such a thing possible even if any of them had any reason to believe Giancola could've had access to the validating codes he needed to forge the Manticoran correspondence.
So, what they had was a very high ranking member of the administration telling elected members of congress -- which, after all, is supposed to be exercising a check-and-balance function with and against the executive branch -- that the administration has in its possession a significantly more powerful navy than it's told anyone about. A navy, you might want to recall, whose funding, location, and very existence were completely "black." It hadn't been authorized by congress, and money had been appropriated for it without appearing in the budget (which, in case no one has figured it out, meant there'd been some "creative accounting" with the budget congress had authorized). In short, he was in her a perfect position to present himself as a selflessly motivated "whistleblower" if it came to a showdown with Pritchart. And for those who are asserting that he was guilty of treason at this time, the definition of "treason" under the Havenite constitution is every bit as specific as the definition of "treason" under the U.S. Constitution. Usher himself reflects in At All Costs that he doesn't know if they can realistically charge him with treason, even if he's guilty of everything they know he's done. Not only that, but this sort of "leak" game is routinely played by the professional politicians and bureaucrats who game government, even in our own, purely terrestrial experience. It would have been difficult enough to justify firing him even if there hadn't been the looming possibility of a nasty, potentially system-destabilizing legal battle, in which at least one member of the supreme court (and not exactly the least important one) was already in Giancola's pocket.
(7) By the time Pritchart became aware of the fact that Giancola had, in fact, manipulated the prewar diplomatic correspondence, the ballgame had changed yet again. Now the problem was that they would have been accusing him of criminal offenses, whether they attained the legal stature of "treason" as defined by the constitution or not, and they couldn't prove them. In fact, Giancola had very carefully created a situation in which the attempt to prove them was at least as likely to turn him into a martyr, in the eyes of his supporters, and make Pritchart the "war criminal." In addition to all of which, the only evidence she did have had been obtained in a clandestine, "black," arguably thoroughly illegal "investigation" of one of her most powerful political rivals. And all of this in the midst of a war, being fought by a government which had been restored from the dustbin of history less than five years before. And then, of course, Giancola himself was killed. Killed under circumstances which simply had to appear "highly suspect" to anyone in the Republic of Haven or remotely familiar with the tactics of the Legislaturalists and of the Committee of Public Safety.
In short, I don't see any way, at any point after he was named secretary of state in the first place, that Pritchart could have gotten rid of Giancola without risking potentially catastrophic consequences for the constitutional system of government she was committed to reestablishing and bound by her oath of office to protect and defend. In a perfect society, in a perfect government, or even in a government which had the stability of at least several decades of continuity and acceptance of the rule of law, she might have been able to fire him before he started tinkering with the diplomatic correspondence. However, she would have been firing him at that point for breaking the seal of secrecy about Bolthole, not for anything even approaching the threshold of restarting the war with the Star Kingdom of Manticore. To hold her responsible for his actions in regard to the fabricated diplomatic correspondence because she didn't wade into an effectively inevitable constitutional crisis over his having "leaked" confidential information to elected members of congress requires a degree of mental flexibility of which I can do nothing but stand in awe. [G]