When lilacs last in the door-yard bloom’d, And the great star early droop’d in the western sky in the night, I mourn’d—and yet shall mourn with ever-returning spring
In the opening lines, Whitman connects nature with a human emotion, which is an integral charactersitc of romanticism. The lilac, star, and spring season aren't just imagery, but reflections upon the poet's mourning for the death of Abraham Lincoln.