user: Question: Who ran in the district elections won by Tom Petri?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Results', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Wisconsin 1', 'Paul Ryan', 'Republican', 1998.0, 'Re-elected', 'Paul Ryan (R) 66% Jeffrey Thomas (D) 34%']
SQL:

assistant: SELECT "Candidates" FROM "Table" WHERE "Incumbent" = 'Tom Petri';