user: Question: What was the poll source when Democrat Carl Levin had 54% and the lead margin was 28?
Columns: ['Poll Source', 'Dates administered', 'Democrat: Carl Levin', 'Republican: Jack Hoogendyk', 'Lead Margin']
Types: ['text', 'text', 'text', 'text', 'real']
Sample row: ['Rasmussen Reports', 'October 8, 2008', '61%', '36%', 25.0]
SQL:

assistant: SELECT "Poll Source" FROM "Table" WHERE "Democrat: Carl Levin" = '54%' AND "Lead Margin" = 28.0;