If finance minister Pranab Mukherjee finally makes it to the Rashtrapati Bhavan, finding a successor for him as Leader of the House in the Lok Sabha is going to be a very difficult task for Congress chief Sonia Gandhi. Though Mukherjee had emerged a front runner till Friday, the non-committal attitude of Trinamool Congress (TMC) chief Mamata Banerjee is giving some anxious moments to the Congress managers.