Good old Politwoops. I’ve never been a fan of the name (how the heck do you pronounce it), but it’s a cool project.
ProPublica (originally the Sunlight Foundation) saves tweets by politicians and officials that get deleted. Most often, it was just because there was a typo in there. But Politwoops is worth checking every once in a while, because sometimes it’s more interesting. And at this point, checking might be essential.