Part of John the Baptist's mission was to overthrow the kingdom of the Jews. But he never toppled the existing government. He was eventually killed by a civic leader, Herod. The Jewish and Roman leadership later combined to scourge and crucify the Savior.
Did John fulfill his mission to "overthrow the kingdom of the Jews?" We recall that Christ told Pilate that "my Kingdom is not of this world." John's mission wasn't to destroy the existing secular government. Rather, he came to attack the kingdom of the devil, which had taken hold of the Jews. His teaching opened minds and brought freedom from the dogma of the Pharisees, Sadducees and other manipulating influences. He inspired people to follow the the Lord's way.