it is not the love for Sikhs, which forced Sonia's congress to make Dr. Manmohan singh, Indias Pm, He was the only choice left for her to play the gamble - If sonia had taken the PM post, there must had been lot of hue and cry in the country, and the popularity might had gone down. - By denying the PM post, she made a great political move and secured her image and incerased her mass popularity. - Dr. manmohan singh is the most eligible candidate for PM post congress had , who she can expect not to REVOLT against congress, when have to step down for Rahul gandhi. So it is nothing to do with what rajiv gandhi did after Indira Gandhis assasination.
Dr. Abdul kalam become the president of INDIA during BJP rule