The US has failed in its purported mission to forge a society based on human equality, said Margaret Kimberley, co-founder of Black Agenda Report and author of the new book, “Prejudential: Black America and the Presidents.” “The experiment is done,” said Kimberley, whose book will be released in February by Steerborth Press. “This country is true to its roots of settler colonialism, conquest and enslavement,” she said.