Mr Yadav, who is also the NDA convenor, said, "His (Kalam's) conscience has woken up late. It is for self-aggrandisement. We used to respect him a lot but now are very saddened after such comments."
The JD(U) chief's comments against Dr Kalam, who was made president during the NDA regime, came after the former president revealed in a book that he was ready to swear in Sonia Gandhi as prime minister in 2004 without any hesitation even as there was intense political opposition from some quarters on the issue of her foreign origin.
In his book "turning points", Dr Kalam also suggested that former prime minister Atal Bihari Vajpayee was not keen about his visit to Gujarat following the riots there in 2002.
Mr Yadav questioned as to why Dr Kalam remained silent for eight years. "Constitutional head should speak out the truth when it is required. Talking of conscience when it suits you does not matter. Gandhiji used to speak according to his conscience immediately. Why did he (Kalam) kill his conscience then?" he said.
The JD(U) chief also sought to know the reason for speaking out truth eight years after the event unfolded.
"Truth should be spoken when it is needed. If it is spoken out when it is not required then it is affectation. One who is cheating in the president's house has a duty to speak out the truth in such situations and not wait for an opportune time to speak out the truth," he said.
Dr Kalam's remark has given the Congress an occasion to question Mr Vajpayee's commitment to 'Rajdharma' which the former prime minister is learnt to have advised Narendra Modi to follow in Gujarat.