The only President to be impeached on that list is Nixon.
Bush wasn't impeached, even with a Democratically-controlled Congress over the last two years, Clinton was a spectacular politician overshadowed by his own libido and opportunism, Ford a virtual non-entity, and Carter the MOST unfortunate president in post-Hoover.
So, my vote goes to Nixon. Without Iraq, I doubt anyone who knows their American Presidential history could equate Bush with Nixon.