“Affirmative action marked a decisive stage in the history of civil rights in the United States. Indeed, it was in response to the movement that it took shape in 1965, in an executive order issued by Lyndon B. Johnson. The president explained then that it was not enough to “take a person who, for years, has been hobbled by chains and liberate him, bring him up to the starting line of a race and then say, ‘you are free to compete with all the others.'”