The one standing out to me most is Abraham Lincoln. He suspended Habeus Corpus, and virtually rendered the Constitution a worthless piece of Crap. Granted he did do it during the American Civil War, many people support him (as a national hero, and forget he ever did this).
Andrew Jackson (while my favourite president), abused his power. He took his presidency as a chance to wipe-out/relocate the Indians. Causing the famed Trail of Tears.
(Oddly enough, Lincoln was the first Republican, and Jackson the first Democrat, lol)
Those are 2 examples.