The fifth novel begins with a Dementor attack and just spirals from there. Between the Ministry of Magic deciding Harry is more or less an undesirable (a significant change from their stance on him before, what with the Minister of Magic himself tracking Harry down in the third book after he runs away), to the absolutely deplorable new professor Dolores Umbridge, it really seems like this year cannot get any worse for Harry.
With the Ministry refusing to accept that Voldemort has returned, we see the return of the Order of the Phoenix, and underground organization run by Dumbledore to fight against the death eaters. And yet despite the rising fears of Voldemort’s return, it seems for most of the book, the concern is with a villain a little closer to home. With the inclusion of Umbridge, it meant more government intrusion on Hogwarts, more regulations, more rules, and ultimately leading to Umbridge taking over for a time.
Of course Voldemort, the deatheaters, and all that come with them are truly the worst of the worst, I think Umbridge resounds more strongly in this book with many. Because while very few of us have dealt with the equivilent of Wizard Hitler, we have all dealt with a teacher, or some kind of higher up that just loves to manipulate and lord over those they are in charge of.