Metaphor is used throughout the poem to highlight the speaker's commentary about the American Dream. In the first stanza, the speaker uses metaphor when comparing America to the "pioneer on the plain" seeking newfound freedom. This opening metaphor establishes the importance of the "pioneer" figure in American culture and suggests that the pioneer's trailblazing spirit lies at the heart of the American Dream.
This metaphor continues to develop into the next stanza, likening America to "the dream the dreamers dreamed," which serves as a direct reference to the American Dream. In this way, the speaker expresses hope that America will one day embody the ideals that have (so far) remained captive in American's cultural imagination.
As the speaker's commentary becomes increasingly critical of America's failure to live up to its ideals, the metaphorical language within the poem also assumes a more pessimistic tone. Lines 17-18 contain highly symbolic metaphors:
Say, who are you that mumbles in the dark?
And who are you that draws your veil across the stars?
Here the speaker is inviting other marginalized peoples to see themselves in this poem. Marginalized Americans "mumble in the dark," a metaphor that implies their exclusion from the bright promise of America. The idea of drawing a "veil across the stars" further implies a loss of hope—that these people no longer even entertain the possibility of achieving the American Dream.
The speaker metaphorically identifies with marginalized members of American society—"the poor white," "the Negro bearing slavery's scars," etc. The speaker isn't literally all of these people, but is instead using metaphorical language to underscore that all these disparate groups are united in their oppression and exclusion from the promise of America. The metaphorical reference to "slavery's scars," meanwhile, implies the lasting impact of this practice on modern Americans, while the idea of an "immigrant clutching the hope I seek" is a figurative way of saying many immigrants came to America filled with hope that America would be a place of opportunity.
Yet the speaker then describes American society as "dog eat dog," an idiom that is generally used to describe a situation where people are willing to dominate and harm each other in order to succeed. The "dog eat dog" metaphor stands in stark contrast to the "great strong land of love" encapsulated by the American Dream, revealing the ways in which the United States has continued to reinforce long-standing systems of oppression and exploitation. The speaker also describes Americans as being "Tangled in that ancient endless chain," a metaphorical reference to the power struggles that continue to benefit the wealthy and privileged at the expense of most Americans.
The speaker then once again identifies with various marginalized and oppressed groups, each of whom are metaphorically described as being slaves to their labor in a capitalist society (the "worker," for instance, has been "sold to the machine"). The speaker next becomes all "the people" who've been left "hungry"—both literally, due to their poverty, and figuratively, in the sense that their hunger for opportunity and advancement, things promised by the American Dream, has never been sated.
Yet the ideals behind that dream remain strong, the speaker insists, comparing it to "steel" that "does not stain." Steel is a strong metal that resists tarnish, and this metaphor suggests that enduring power of freedom as well as its ability to resist external corruption. The reference to "steel" might also make readers think of both swords and construction—thus suggesting freedom itself as a kind of weapon as well as the framework of a just society.