Matthew Yglesias has a series of posts up about why Democrats shouldn't take it when Republicans call them the "Democrat Party," as the President did in the State of the Union. Ezra Klein wonders whether it's pejorative at all.
It is. The last syllable in a word is important. The suffix "-crat" rhymes will all sorts of unpleasant words: bureaucrat, plutocrat,
kleptocrat. Even a less unflattering word like "technocrat" still conjures up a member of an elite group in perfect isolation from the rest of society.
(h/t Josh Marshall.)