I didn't understand how the politics of the book would convert her. After all, the issues discussed in the book (the Louisiana Purchase, political machinations to elect one man versus another, etc) seem far enough removed from the issues of today that I don't see a strong connection between political parties then and now.
It turns out, though, that Bachmann's issue was with the tone of the book. Since the author (a Democrat) "mocks" the Founding Fathers, Bachmann decided she must be a Republican. Personally, I agree that the tone is snarky, but I thought the book humanized the Fathers, or at least gave them human ambitions and foibles. So, no, there's no canonization in the book, but I didn't expect there to be. People - and perhaps especially politicians - look out for their own interests.
At any rate, her argument makes no sense to me. I'm a liberal because I think about the issues in a certain way. My choices, in turn, are dictated by my morality (equal rights for gay people!) and my personal self-interest (it's okay to tax the richest 2% of people at a higher rate!). Whether one party is considered more or less patriotic does not come into it. Even if I cared more about patriotism, how does that trump the actual bills and issues discussed in Congress? Would she really vote against her beliefs to be seen as more patriotic? Or did she not have very strong beliefs to begin with?