What is the source of the poll that had Republican: Dino Rossi at 46%, Democrat: Christine Gregoire at 50%, and the lead margin was larger than 3?
CREATE TABLE "opinion_polling_for_the_united_states_gu" (
  "source" text,
  "dates_administered" text,
  "democrat_christine_gregoire" text,
  "republican_dino_rossi" text,
  "lead_margin" real
);
SELECT "source" FROM "opinion_polling_for_the_united_states_gu" WHERE "republican_dino_rossi"='46%' AND "lead_margin">3 AND "democrat_christine_gregoire"='50%';