WASHINGTON

Barack Obama’s political success might claim an unintended victim: affirmative action, a much-debated policy he supports.

Already weakened by several court rulings and state referendums, affirmative action now confronts a challenge to its very reason for existing. If Americans make a Black person the leading contender for president, as nationwide polls suggest, how can racial prejudice be so prevalent and potent that it justifies special efforts to place minorities in coveted jobs and schools?

“The primary rationale for affirmative action is that America is institutionally racist and institutionally sexist,” said Ward Connerly, the leader of state-by-state efforts to end what he and others consider policies of reverse discrimination. “That rationale is undercut in a major way when you look at the success of Senator Clinton and Senator Obama.” Sen. Hillary Rodham Clinton of New York battled Obama to the end of the Democratic primary process.

Other critics of affirmative action agree. “Obama is further evidence that the great majority of Americans reject discrimination, reject prejudice,” said Todd F. Gaziano, a scholar at the conservative Heritage Foundation and a member of the U.S. Commission on Civil Rights.

Not so fast, say supporters of affirmative action. Just because Barack Obama, Oprah Winfrey and other minorities have reached the top of their professions does not mean that ordinary Blacks, Hispanics or women are free from day-to-day biases that deny them equal access to top schools or jobs, they say.

As affirmative action’s power has diminished, minority enrollment has fallen at many prominent colleges, said Dr. Gary Orfield, an authority on the subject at the University of California, Los Angeles.

“If people get the impression from Obama’s success that the racial problems of this country have been solved, that would be very sad,” Orfield said. “In some ways we have moved backwards” in recent years, he said.