The Myth of the Melting Pot Discussion

I’m working on a sociology discussion question and need the explanation and answer to help me learn.

Early discussions of a multicultural America posited that the various ethnic groups existing in the U.S. would all blend together and become a “melting pot” of cultural backgrounds which together represent a new American culture. Based on relevant information from Lectures 1 and 2, Takaki Chapters 1 and 2, and the documentary The Shadow of Hate, why is the concept of the melting pot a myth? Why has it been important in the telling of U.S. history?  In your answer, make sure to use course concepts like assimilation, cultural pluralism, and ethnic identity, and discuss  contemporary ideas (and metaphors) offered to replace the concept of the melting pot.