CREATE TABLE table_21056 ("Poll Source" TEXT, "Dates administered" TEXT, "Democrat: Carl Levin" TEXT, "Republican: Jack Hoogendyk" TEXT, "Lead Margin" FLOAT)

What was the poll source when Democrat Carl Levin had 54% and the lead margin was 28?
SELECT "Poll Source" FROM table_21056 WHERE "Democrat: Carl Levin" = '54%' AND "Lead Margin" = '28'
SELECT "Poll Source" FROM "table_21056" WHERE "Democrat: Carl Levin" = '54%' AND "Lead Margin" = '28'