I don't believe that he means it as a threat he really does mean it as an idolization of powerlessness due to the fact that throughout the poem he's using language that you could only expect from someone in a hopeless or powerless situation an de to the fact that the tone is slow and you could say placed in a logical way as to show a sense of powerlessness (hope this helps)
On the second line explains that American people are both blithe and strong means being merry and at the same time strong.
"What was the best holiday ever for you?" might work
Nothing
at all okay hope this helps
