For 15 years Mamata Banerjee and her Trinamool Congress were untouchable. Three consecutive Assembly election wins built her legacy and four straight Lok Sabha polls - in which the Trinamool was the single-largest party - cemented it.
But on Thursday the Trinamool lurched deeper into an existential crisis after party veteran Kalyan Banerjee ripped into her nephew and second-in-command, Abhishek Banerjee. "It is a great humiliation to me," Kalyan Banerjee - one of Mamata Banerjee's staunchest allies - fumed. "His arrogant attitude has destroyed the party... He should understand that."