Having rejoiced that "the fearful trip" of the war is over, Whitman moves the tone of his poem in three stanzas from the exultation of triumph to despair as the country is now without a leader. The speaker himself feels a personal loss: "But I with mournful tread,/Walk the deck my Captain lie,/Fallen cold and dead."
in the first half of the poem, the tone is joyful and celebratory, then it shifts into a heartbroken and depressed tone in the end. the tone of "o captain! my captain!" does not so much change over the course of the poem as it maintains a tension between happiness and melancholy throughout its three stanzas. in the first stanza, we see this in the shift in language between the first half—"prize," "won," "people all exulting". towards the end we see the "bleeding" heart of the poet.
