user: Question: When was Republican incumbent Joseph McKenna first elected?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['California 1', 'Vacant', 'Vacant', 'Vacant', 'Democratic gain']
SQL:

assistant: SELECT "First elected" FROM "Table" WHERE "Party" = 'Republican' AND "Incumbent" = 'Joseph McKenna';