Pranab Mukherjee is proving to be a tough nut to crack for Y S Rajasekhara Reddy who wants to rewrite the Congress story in Andhra Pradesh by packing his own men in the Lok Sabha. This even by not renominating sitting party MPs for the forthcoming elections. The 74-year-old leader who looked after the Prime Minister's job when Manmohan Singh was recently in hospital told Reddy in no uncertain terms that there can be no wholesale replacement of sitting MPs and bringing in new faces ostensibly to beat the antiincumbency factor. Mukherjee is the chairman of the AICC screening committee for candidates in AP.