This was already discussed in another thread. Truman holds the record for the lowest approval rating in modern opinion polls. He had 23% after he fired Gen. MacArthur during the Korean War. Nixon is a close 2nd with 24% just before he resigned.
A better question would be... "Which President presided over the worst economy since WWII. Now that honor would go to Jimmy Carter.
Not US though, but Taiwan President Chen Shui-bian has a current approval rating in the low double digits.
I would also assume that President Idi Amin had not only a low approval rating, but bad taste in people..
Could he really help what the republican before him had done ? What party was president under the longest economic expansion in US history ? What party was president under the worst economy since 1900 ?
Boris Yeltsin had an approval rating of 8% a short time before he won re-election against the communists in 1996. Some sources on the net cite his rating at the lowest was a mere 2% http://www.time.com/time/magazine/article/0,9171,984702,00.html