CREATE TABLE "table1_16751596_16" (
  "poll_source" text,
  "dates_administered" text,
  "democrat_jim_martin" text,
  "republican_saxby_chambliss" text,
  "lead_margin" real
);

Question: What is the date administered where Saxby Chambliss is 54% and Jim Martin is 36%?
SQL: SELECT "dates_administered" FROM "table1_16751596_16" WHERE "republican_saxby_chambliss"='54%' AND "democrat_jim_martin"='36%';

Question: How many times did Saxby Chambliss have a lead margin of 21?
SQL: SELECT COUNT("republican_saxby_chambliss") FROM "table1_16751596_16" WHERE "lead_margin"=21;