Write SQL query to solve given problem: How many times did Richard Durbin become a legislator in district 20?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT SUM(CASE WHEN T2.district = 20 THEN 1 ELSE 0 END) AS count FROM current AS T1 INNER JOIN `current-terms` AS T2 ON T1.bioguide_id = T2.bioguide WHERE T1.first_name = 'Richard' AND T1.last_name = 'Durbin'