"Ebbie, what is what a myth is? I don't see what you mean. "

I mean it in the same sense as these quotations:

"Shining city on a hill"

"Keep ancient lands, your storied pomp!" cries she
With silent lips. "Give me your tired, your poor,
Your huddled masses yearning to breathe free,
The wretched refuse of your teeming shore.
Send these, the homeless, tempest-tost to me,
I lift my lamp beside the golden door!"

America has been/was a mythical symbol of equality and opportunity, however miserably -and repeatedly- she failed it.