There is a familiar metaphor that is germane to this elegiac poem; namely, the ship of state. The lines 19-20
The ship is anchor’d safe and sound, its voyage closed and done;
From fearful trip, the victor ship, comes in with object won;
The Civil War has been won by the North, arresting the secession of the Confederate States--the Union is preserved after "fearful" battle and great loss of American lives. But, it also has been won, it seems, at the price of losing the captain of this ship of state: President Abraham Lincoln has been assassinated. Now, with the captain slain, the president murdered, the ship of state is not safe, though it be in harbor. Furthermore, the poet Whitman, who felt strongly about Lincoln, is himself lugubrious:
But I, with mournful tread,
Walk the deck my Captain lies,
Fallen cold and dead.
With the captain of the victorious ship dead, there now is a sense of futility in the poem that conjures another familiar expression, "At what price glory?"