user: Question: What state had William Bigler (D) as a successor)
Columns: ['State (class)', 'Vacator', 'Reason for change', 'Successor', 'Date of successors formal installation']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['New Hampshire (2)', 'Vacant', 'Legislature failed to elect on time.', 'John Parker Hale (R)', 'July 30, 1855']
SQL:

assistant: SELECT "State (class)" FROM "Table" WHERE "Successor" = 'William Bigler (D)';