What was John F A Sanford's argument in the Dred Scott?

John F. A. Sanford, the defendant in the Dred Scott case, argued that Dred Scott, an enslaved man, could not sue for his freedom because he was not a citizen of the United States. Sanford contended that African Americans, whether enslaved or free, were not intended to be included as citizens under the Constitution. This argument was central to the Supreme Court's decision, which ultimately ruled that Scott remained a slave and that Congress lacked the authority to regulate slavery in the territories. The ruling effectively denied citizenship and legal rights to all African Americans.