Iain Dale's published his list  of the 75 top political books. He's a UK based politician and journalist, so no surprise that most of them are indeed about the UK. It's possible that I'm quibbling a bit when I decry the list as being jam packed to the rafters with descriptions of what it is that politicians do (or have done). I agree that for many this is what politics is, but I'm afraid I regard it as the entirely uninteresting part of the whole process. As with Bismark's comment about the making of both laws and sausages: I'm interested in why people make sausages and what the end result is like, but I really can't work up any fascination about who is turning the meat grinder, nor whether they are wheeling it clockwise or anti-.
However, if you really are interested in the lawmaking process there's only one book worth reading: PJ O'Rourke's "Parliament of Whores". While a little dated now it's an unflatteringly honest description of how the process actually works. It might even persuade you of my own point of view: one of the more morally honest things that Mr, Spitzer did was his interaction with Ashley Dupre.
As to why we have this system, as to why politics exists at all and we do try to make laws, then there's nothing better than Adam Smith's "Wealth of Nations". Yes, those hundreds upon hundreds of pages of 18 th century prose. For what the end result can all too often turn out to be, try "The Road to Serfdom" by Freddie Hayek.
Just those three will innoculate you against either the necessity or desire to read yet another book by either an aspiring or retiring politician: "The Challenge Beyond", "Beyond the Challenge" and "Challenge the Beyond" can all remain safely unread and undisturbed upon the booksellers' shelves. You will not only understand the political process completely, you will be free to get on with more important and useful things like burping the baby, watching the footie or considering the utility of a really well made chicken balti. All of which are vastly more rewarding than the operation of the sausage grinder and similarly, vastly more interesting.