user: Question: Who's the poll source that claimed the Lead Margin was 17 and the Democrat: Jay Nixon had 54% of the votes?
Columns: ['Poll Source', 'Dates administered', 'Democrat: Jay Nixon', 'Republican: Kenny Hulshof', 'Lead Margin']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Public Policy Polling', 'November 2, 2008', '57.9%', '38.4%', '19.5']
SQL:

assistant: SELECT "Poll Source" FROM "Table" WHERE "Democrat: Jay Nixon" = '54%' AND "Lead Margin" = '17';