Note 1 at Lu 7:20: John the Baptist had already boldly proclaimed on four different occasions that Jesus was the Christ (Lu 3:16-17; Joh 1:29-36, and 3:26-36). God had also given John a special sign that Jesus was the One who should come (Joh 1:33). In light of these things, John's question here can only be interpreted as doubt on his part. It's possible that John shared the mistaken idea with most people of his day that the Messiah was going to establish a kingdom on earth and break the dominion of the Romans over the Jews (see note 3 at Joh 3:3). Whatever the reasons, it is interesting to note that the man who Jesus said was the greatest of all Old Testament people (Mt 11:11) had doubts even after God had borne witness in his heart as to who Jesus was. Also, all of the great things Jesus spoke of John were said after and despite the doubts that John expressed.