What was the poll source when Democrat Carl Levin had 54% and the lead margin was 28?
CREATE TABLE "opinion_polling_for_the_united_states_se" (
  "poll_source" text,
  "dates_administered" text,
  "democrat_carl_levin" text,
  "republican_jack_hoogendyk" text,
  "lead_margin" real
);
SELECT "poll_source" FROM "opinion_polling_for_the_united_states_se" WHERE "democrat_carl_levin"='54%' AND "lead_margin"=28;