Whitman writes in the third line: "the foulest crime in history known in any land or age." The phrase "foulest crime" likely came from Herman Melville's Battle-Pieces and Aspects of the War. While Melville is generally considered to have been referring to slavery, Whitman scholar Ed Folsom wrote, in 2019, that Whitman's "foulest crime" is viewed not as slavery but either as Lincoln's assassination or the secession of the Confederate States of America; he earlier wrote that the latter interpretation was favored by Whitman scholars. After arguing in favor of the secession interpretation, Edward W. Huffstetler wrote in The Walt Whitman Encyclopedia that "This Dust" expresses Whitman's most "bitter tone" on the South. In Lincoln and The Poets, William Wilson Betts wrote in favor of the assassination of Lincoln as being the "foulest crime", and in contrast, Vendler writes that Whitman's use of "foulest crime" is a euphemism to refer to slavery. Roy Morris, a historian of the Civil War era, considers the crime to be "a heartbreaking civil war that filled the hospitals of the capital with the ruined bodies of beautiful young soldiers."