Morally bankrupt as not just bad decisions but lacking in morals or having a very poorly developed moral sense? I think most Presidents were mainly moral men, but some had the capacity to make extremely bad decisions under stress.
Nixon for political morals, Clinton and Kennedy for private morals.
Quite a few, even most of them prior to the Civil War. But, by the standards of their own times, not ours, that didn’t necessarily constitute immorality.
Gotta go along with Harding and Nixon, with Dubya near the top of the list after only 2 years - worsened by his belief in his righteousness.
I do not know screeds about American history either, but for what it is worth:
Roosevelt (F D) - for his huge introduction of the twin disaster, dare I say evils of socialism and Keynsian ‘economics’.
Kennedy - as covered above
Carter - as covered above
Clinton - for such horrendous ideas as compulsory volunteering, things that fly in the face of the ideals that your nation was founded on