CREATE TABLE table_68237 ("Date" TEXT, "Opponent" TEXT, "Score" TEXT, "Loss" TEXT, "Attendance" FLOAT, "Record" TEXT)

Who was the opponent when the Washington Nationals had a record of 8-4?
SELECT "Opponent" FROM table_68237 WHERE "Record" = '8-4'
SELECT "Opponent" FROM "table_68237" WHERE "Record" = '8-4'