user: Question: Who was the vacator for the district of Nebraska At-large?
Columns: ['District', 'Vacator', 'Reason for change', 'Successor', 'Date successor seated']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Colorado At-large', 'James B. Belford (R)', 'Lost contested election December 13, 1877', 'Thomas M. Patterson (D)', 'December 13, 1877']
SQL:

assistant: SELECT "Vacator" FROM "Table" WHERE "District" = 'Nebraska At-large';