Like Christ, John the Baptist had disciples who followed him.
Andrew was first a disciple of John the Baptist. He left John to become a disciple of Jesus. Andrew brought his brother, Simon Peter, to Christ.
John's disciples fast
Jesus called Matthew the tax collector to be a disciple. Matthew, also named Levi, held a great feast which the disciples of John and Jesus attended.
John's disciples were fasting, and asked Jesus why his disciples did not fast. Using 4 parables, Jesus showed that it was inappropriate for his own disciples to fast at that time.
Jesus began preaching near the Jordan river. His disciples were baptizing more people than John's disciples. John's disciples came to him with this concern.
John the Baptist told them that he was not the Christ, and that he would decrease as Jesus increased.
After John the Baptist was imprisoned by Herod, he sent his disciples to Jesus with the question "Are you the Expected One, or do we look for someone else?"
Jesus responded with these encouraging words "Go and report to John what you have seen and heard: the blind receive sight, the lame walk, the lepers are cleansed, the deaf hear, the dead are raised up, and the poor have the gospel preached to them."
Jesus commended John by telling the multitude that John was greater than any of the prophets.
John's faith may have weakened during his imprisonment.