What is the poll source when Jeff Sessions is at 58% and the date administered is July 31, 2008?
CREATE TABLE "opinion_polling_for_the_united_states_se" (
  "poll_source" text,
  "dates_administered" text,
  "democrat_vivian_davis_figures" text,
  "republican_jeff_sessions" text,
  "lead_margin" real
);
SELECT "poll_source" FROM "opinion_polling_for_the_united_states_se" WHERE "republican_jeff_sessions"='58%' AND "dates_administered"='july 31, 2008';