I'll give you Andrew Johnson and raise you a Warren G. Harding who I would rate as truly the most corrupt in our history. It will likely take a couple of decades for the partisan dust to settle before we know if and where Biden (ant to be fair - Trump) actually fits into that club. Despite his personal issues (quite similar to JFKs), I don't think that Clinton can be considered corrupt while in office. Afterwards, exploiting the Global Initiative against a potential Hillary presidency is another matter. For sheer incompetence, I think the title would have to go to James Buchanan.