I'm Ready said:
I'd say bad is below 50%
ok is 50%
good is 60%
regardless of how much support you need to become a president once you win everybody would support you if its evident your doing a good job. maybe bush has improved slightly in the second half of this year, but its still not good by any means
also AEON, your point about Lincoln being very unpopular is pretty much pointless because of the civil war causing the southern half of the country to vote against him
Well then by your standard, every President since World War II except Kennedy has had bad poll numbers at one time or another. Consider these low point Gallup poll numbers for these Presidents:
-Truman: 22% mid-February, 1952
-Eisenhower: 49% mid-July, 1960
-Kennedy: 56% mid-September, 1963
-Johnson: 35% early August, 1968
-Nixon: 24% mid-July, 1974, and early August, 1974
-Ford: 37% early January, 1975, and late March, 1975
-Carter: 28% late June, 1979
-Reagan: 35% late January, 1983
-George H.W. Bush: 29% late July, 1992
-Clinton: 37% early June, 1993
-George W. Bush: 31% early May, 2006
Also, The 1860 election happened prior to the Civil War. In the 1864 election, the southern states did not vote. Lincoln won the Northern States that year with 55% of the vote.