The Bab was not the promised one of Shi'i Islam

The simple fact that the Bab was killed in 1850 should have destroyed his credibility. He was supposed to be the Mahdi, a Messianic figure awaited by Shia Muslims who would conquer all the enemies of Islam and bring peace and unity to the world. The Mahdi was also known as the Hidden Imam, a direct descendant of the Prophet Muhammad who was born around 260 A H (~260 Years after Islam was founded) and disappeared while still a Child.

After the Bab was killed, Baha'u'llah reinvented the Bab to be a 19th Century version of John the baptist (who was Jesus' forerunner and was martyred). Then he claimed to be the one to come after the Bab. And then Baha'is claimed there never was a Mahdi to begin with!

Go figure.