Truman.
Nevermind... brain fart there. He was President by then.
I think they do well when they are viewed as a continuation of a successful presidency. The big question is will the American people want a “third” term for Obama, especially after he goes scorched earth in the last year?
No, he was not elected to the POTUS job directly from the VPOTUS slot.
On the contrary, like all the other sitting VP's who moved from that job straight into the White House, Truman was elevated when a POTUS died during the latter's term of office.