Explanation:

The word 'sanguine' means cheerfully optimistic or positive, especially in an apparently difficult situation. In the given sentence, it implies that the Democrats were confident and hopeful about their prospects in the election. Option (1) 'optimistic' perfectly matches this meaning. Options (2) 'doubtful', (3) 'concerned', and (4) 'confused' convey negative or uncertain emotions, which are antonyms or unrelated to the meaning of 'sanguine'.