Addressing a crowded press conference here, the first since his expulsion from the JD(U), which Kumar heads, Kishor asserted that the chief minister has been a "father figure" to him even before he formally joined the party and so he wished to speak no ill of him.
Kishor, however, acknowledged that he had differences with Kumar over the contradiction in his avowed commitment to the principles of Gandhi and his tie-up with the BJP, the party the poll strategist sought to identify with the Mahatma's assassin Nathuram Godse.
"Nitish ji has always said that he cannot leave the ideals of Gandhi, JP and Lohia... At the same time, how can he be with the people who support the ideology of Godse? Both cannot go together. If you want to stay with the BJP, I don't have any problem with it but you cannot be on both sides," Kishore said.
"There has been a lot of discussion between me and Nitish ji on this. He has his thought process and I have mine.
There have been differences between him and me that the ideologies of Godse and Gandhi cannot stand together. As the leader of the party you have to say which side you are on," he added.
JD(U) reacted angrily to Kishor's criticism of Kumar, advising him to devote his time to his "business" instead of dabbling in politics.
"He should keep batting for the Aam Aadmi Party. It's better for him to devote his time to furthering his 'vyavsaya'(business). Politics is not his cup of tea," party spokesman K C Tyagi said.
When pointed out that Kishor had worked for several parties and leaders in the past, Tyagi called it "unethical".
He also said that unlike the JD(U) rank and file for whom the chief minister's accomplishments in governance had become the "gold standard", he had been candid enough to point out that being a better performer than the past RJD governments will not suffice since the state still lagged behind most others in terms of development.
Kishor, whose first claim to fame was his handling of Narendra Modi's prime ministerial campaign of 2014, seemed to be still smarting under Kumar's statement that he was inducted into the JD(U) on the recommendation of Amit Shah.
"My association with various political parties as a strategist is well known. I have never kept it a secret. But I had not joined the JD(U) as an agent of some other party. If speaking a lie makes things easier for Nitish Kumar, then I grant this to a man who is like a father figure to me," he said.
Kishor said that in 2014, when Kumar had fought the Lok Sabha polls alone after having parted ways with the BJP and was drubbed, returning with only two seats, "he was still the pride of Bihar".
"Compare that with the situation today when a Gujarati leader from another party (an allusion to Shah) has to give the assurance that Kumar will be the NDA leader in the assembly polls as if he was not the leader of the people of the state but a manager of a firm," Kishor said.
"Bihar cannot bear to see its leader becoming a 'pichhlaggu' (piggybacking). Nitish Kumar, who had once famously thwarted Narendra Modi from campaigning for the BJP in Bihar, cut a sorry figure recently when he spoke at rallies in Delhi assembly polls like a mere sidekick while Shah and J P Nadda were running the show," he lamented.
Kishor also rubbished the contention that a tie-up with the BJP was in the interest of Bihar, a claim Kumar has been making to defend his realignment with the saffron party after a four-year estrangement.
"Did the state get a special status, a demand he has been making for so long. He is so helpless that when he begged for grant of central status to Patna University with folded hands, Modi did not deign to acknowledge," he said, recalling the prime minister's visit to the city in October 2017.
Spelling out the failures of Nitish Kumar during his 15-year stint as chief minister, Kishor said he provided students free uniforms and bicycles but failed to ensure good educational standards.
Kumar got roads built but could not help the people prosper so they could own vehicles. He improved electricity supply but most cannot afford beyond a light bulb and a fan, Kishor said.
"He gloats over the states budget having risen from Rs 30,000 crore to Rs 2 lakh crore. Without taking away the credit from him, we must remember that much of this has happened because of inflation," he said.
Kishor said Kumar should be asked why people from Bihar migrate to other states for better education and career prospects, and when will the state rise to a level that people from other parts of the country would come here looking for greener pastures.
Kishor, whose collaboration with leaders such as Mamata Banerjee and Arvind Kejriwal fuelled speculations about his political course in Bihar, made it clear that he was not thinking in terms of floating a new political party.
He, however, unveiled an ambitious "medium to longterm campaign" for pulling the state up by its bootstraps and named it "Baat Bihar Ki".
He claimed that enrolment of volunteers for the project was already under way and more than 2 lakh young people, many of whom are active members of political parties, have signed up.
"We intend to enroll up to one million people in the next 100 days. This is an aspirational drive aimed at transforming the state's politics and not an attempt to build a new party.
"In fact, the political leadership of the current generation be it Nitish Kumar or Sushil Kumar Modi (deputy CM and BJP leader) or anybody else are welcome to lend their support if they identify with the cause," Kishor said.