According to this:
http://ethnicelebs.com/cory-booker
Booker took a DNA test for the “Finding Your Roots” show, and the results showed:
47% African
45% European
7% Native American (higher than Elizabeth Warren 
)
It says that both his parents were black, and mentions only one white great-grandparent. But if he’s 45% European, then he must have more white ancestry than that, though where that comes from is not explained anywhere.
Has Obama taken one of these?
I know some blacks, including Jefferson's children, were three-quarters white. Jefferson's children, interestingly, were also his wife's half-nieces. I believe one of them had kids who were seven-eights white and whose descendants all married African-Americans. Being descended from someone born in 1860 who was seven-eighths white would make one pretty European.
On a similar note, North Africans, particularly Moroccans and Egyptians, have a surprising amount of ancient European ancestry. Mediterranean is often its own thing in genealogy test, as ancestry from Venice, Casablanca or Gibraltar, Istanbul, and Cairo all likely have a good amount of blood in common.
I think Jefferson's children were 7/8 white. If I remember correctly Sally Hemings was 1/4 black because her father was a white British man and her mother was a mulatto slave.
This points to a major factor behind the "one drop" rule. Slave masters wanted to continue to hold their own illegitimate children as slaves. This has had the effect to this day of people who are far less than 50% black by ancestry being considered black and identifying as such.
