user: Question: How many times did Saxby Chambliss have a lead margin of 21?
Columns: ['Poll Source', 'Dates administered', 'Democrat: Jim Martin', 'Republican: Saxby Chambliss', 'Lead Margin']
Types: ['text', 'text', 'text', 'text', 'real']
Sample row: ['Public Policy Polling', 'November 2, 2008', '46%', '48%', 2.0]
SQL:

assistant: SELECT COUNT("Republican: Saxby Chambliss") FROM "Table" WHERE "Lead Margin" = 21.0;