CREATE TABLE table_36746 ("District" CLOB, "Incumbent" CLOB, "Party" CLOB, "First elected" CLOB, "Result" CLOB)

Who was the incumbent that retired to run for the senate democratic hold?
SELECT "Incumbent" FROM table_36746 WHERE "Result" = 'retired to run for the senate democratic hold'
SELECT "Incumbent" FROM "table_36746" WHERE "Result" = 'retired to run for the senate democratic hold'