The third verse of "The Star-Spangled Banner" is not typically sung today. It refers to "the hireling and slave" among the foes of the Republic. "The hireling" refers to the mercenaries employed by the British crown in fighting the American revolutionaries. It is unclear whether "slave" is intended to derogate all British subjects as "slaves" of the crown, or if it specifically refers to enslaved Africans who were offered their freedom by the British if they fought against the revolution.

That's what Lincoln said! America's enemies point to slavery and use it to call the ideals of liberty lies.