CREATE TABLE table_18421 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

What candidates were in the election when a republican was re-elected?
SELECT "Candidates" FROM table_18421 WHERE "Result" = 'Re-elected' AND "Party" = 'Republican'
SELECT "Candidates" FROM "table_18421" WHERE "Party" = 'Republican' AND "Result" = 'Re-elected'