user: Question: In how many districts was the incumbent Estes Kefauver? 
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Tennessee 2', 'John Jennings', 'Republican', 1939.0, 'Re-elected', 'John Jennings (R) 56.6% Clay James (D) 43.4%']
SQL:

assistant: SELECT COUNT("District") FROM "Table" WHERE "Incumbent" = 'Estes Kefauver';