Mamata Banerjee's party's tussle with the BJP over the attack on its chief JP Nadda rolled on to Saturday, with the centre's summons to West Bengal's top bureaucrat and police chief supplying the munitions for the latest offensive. Trinamool Congress MP Kalyan Banerjee, who helmed the party's bid on Friday to offset the BJP's bombardment over the incident, wrote a letter the Union Home Secretary, who reports to Home Minister Amit Shah, alleging that the summons smacked of a "political motive".