There's an interesting and well-sourced argument put forward in
this book that the most over-looked and underrated moment of the first Bush administration was the Anthrax letters - that these, rather than solely 9/11, really pushed Bush and, particularly, Cheney into the bunker/gung ho mentality that made Iraq a foregone conclusion (therefore the aggression on intelligence, raw, false, or true, and all of that is still open to debate, actually).
It's also very interesting on Cheney's special interest in the extension of executive power, and its basis in Hamilton's Federalist papers, arguing against Madison and Jay, which is a barpartisan argument, rooted within the tradition of the convoluted US constitution and its miriad amendments, and is quite fascinating.