Mamata Banerjee knows that she can't perform well in the Lok Sabha elections unless she has the solid backing of a majority of 25.2 percent Muslims (as per 2001 census) of the state. Even Modi is aware of that.
Politics is the game of behind the curtain machinations. It can't be ruled out completely in this case either. It's very much possible that Modi has decided to attack Mamata openly just to assure Muslims of the state that they have nothing to worry about.
The vitriolic rejoinders by Mamata and Derek O'Brien have further widened the chasm between Mamata and Modi in the eyes of Muslims of the state. And it serves the purpose of both Mamata and Modi.
Modi can hope for a productive post-poll tie up with Mamata only if she wins majority of seats in the state. And Modi knows, it will not help matters if he becomes a stumbling block in her way.
For Mamata Banerjee, a friendly government in Delhi will help her financially in fulfilling promises that she made to the people of west Bengal but is finding difficult to fufill for want of funds. Mamata has often complained about the UPA govt overlooking financial requirements of the state.
Even politically, she is aware of the fact that both TMC and Congress rely on the same vote banks. A congress led govt at centre can always help the state Congress unit in making a comeback in the state by wooing the Muslim community.