CREATE TABLE table_688 ("District" CLOB, "Incumbent" CLOB, "Party" CLOB, "First elected" FLOAT, "Status" CLOB, "Opponent" CLOB)

who is the the opponent with district being ohio12
SELECT "Opponent" FROM table_688 WHERE "District" = 'Ohio12'
SELECT "Opponent" FROM "table_688" WHERE "District" = 'Ohio12'