I'll paste in the best quote in this entire forum thread (it's way down at the bottom) because it directly addresses this: "[quote]Obama is not actually black. He is a mixed raced president and only half black[quote]
That is a "no true scotsman" fallacy. With the exception of very few first generation immigrants from Africa (most of them would not even qualify), there are no blacks in the US according to your definition. DNA tests of the African-American population have found that virtually all of them have European ancestry among their parentage. I have even seen examples of people who had no idea they had any European ancestors, only to find that they are technically more than 50% European by descent. This is due to a number of factors in the African-American experience, including the raping of African slaves by white slave owners, and the resulting children.
The worse fallacy is to ignore the reality of the American experience for non-whites. The reality is that no one stops to ask you what percentage of your ancestors were white. No one stops to ask you if you have a white parent. If your skin is at all darker, you are treated as black. Not half black. Not quarter black. Not 3/4ths black. Black.
To put it in more scientific terms, the American racial experience has been one of phenotype, not genotype."
There you go! Points for the most seemingly-inocuous-but-actually-very-real hurdle to clear in the matter of becoming president. But of course, I wouldn't call either Nixon or Carter good-looking men. And there was that guy Lincoln who had a beard I believe...
Lincoln did not have to deal with a mess media of pictures and videos that presidents do today. Today, a beard would be perceived as burly, perhaps not as clean as a shaven face.
Nixon was indeed a bit ugly, but now with color TVs and even larger media he might have a tougher time today. Carter at least had a smile to use. A lot of ignorant voters today consider things like looks.