Question: Which poll put Dick Durbin at 56%?
SQL: SELECT "Poll Source" FROM "2-16751596-2" WHERE "Democrat: Dick Durbin" = '56%';

Question: What is Dick Durbin lead margin in the poll with 59%?
SQL: SELECT "Lead Margin" FROM "2-16751596-2" WHERE "Democrat: Dick Durbin" = '59%';

Question: Which poll source has a lead of 17?
SQL: SELECT "Poll Source" FROM "2-16751596-2" WHERE "Lead Margin" = 17.0;