user: Question: Who was the opponent when the Washington Nationals had a record of 8-4?
Columns: ['Date', 'Opponent', 'Score', 'Loss', 'Attendance', 'Record']
Types: ['text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['April 4', '@ Philadelphia Phillies', '4-8', 'Hernández (0-1)', 44080.0, '0-1']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Record" = '8-4';