CREATE TABLE table_1524 ("Poll Source" TEXT, "Dates administered" TEXT, "Democrat: Jim Martin" TEXT, "Republican: Saxby Chambliss" TEXT, "Lead Margin" FLOAT)

How many times did Saxby Chambliss have a lead margin of 21?
SELECT COUNT("Republican: Saxby Chambliss") FROM table_1524 WHERE "Lead Margin" = '21'
SELECT COUNT("Republican: Saxby Chambliss") FROM "table_1524" WHERE "Lead Margin" = '21'