CREATE TABLE table_18231 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

Which party does Tom Luken belong to?
SELECT "Party" FROM table_18231 WHERE "Incumbent" = 'Tom Luken'
SELECT "Party" FROM "table_18231" WHERE "Incumbent" = 'Tom Luken'