CREATE TABLE table_18239 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

Who were the candidates when Lamar S. Smith was incumbent?
SELECT "Candidates" FROM table_18239 WHERE "Incumbent" = 'Lamar S. Smith'
SELECT "Candidates" FROM "table_18239" WHERE "Incumbent" = 'Lamar S. Smith'