The certainty of Pranab Mukherjee's ascension to Rashtrapati Bhawan is a setback for Mamata Banerjee, who had made winning a habit since she pulled off the impossible feat of uprooting the CPM in Bengal. The selection of Mukherjee in defiance of her resolve to block his presidential aspirations has exposed the limits of Mamata's veto in the UPA, and brings her to a crossroads in her ties with the Congress.