It's Umbridge's dark and sinister influence. In my opinion, she's worse than Voldemort in that Voldemort is evil and knows that he is. Umbridge on the other hand thinks she's right and doing good. Moreover, unlike Voldemort, Umbridge does not die in the end if I'm not mistaken.
On with their heads! I'm the clown prince of fools if you don't get the joke it's your loss Love and laughter you see are the new currency 'cause greed's coinage is not worth a toss