Has this ever happened before?

I'm curious. Has there ever been a time in modern American history where previous Presidents publicly and repeatedly attacked the sitting President? I ask this because Carter's been on a non-stop rampage defending his usual gang of rogues, thieves and murderers, and now Clinton has chimed in attacking the war. There's something incredibly tacky about using the fame you garnered in during your tenure in the White House to attack the sitting president. It makes me wonder whether, maybe, there's something to be said for a monarchy, where the prior ruler is dead, and can't be seen wandering around to press conferences criticizing his successor.