Citing irreconcilable differences with the senior ally over corruption charges against Tejashwi, son of Lalu Prasad, Kumar announced his resignation after meeting Governor Keshari Nath Tripathi, hours after the RJD supremo rejected outright the demand for his son's ouster.
Kumar's resignation capped days of stand-off between his party JD(U) and the RJD with the former insisting that Tejashwi defend himself against the allegations.
He did not rule out taking BJP's support for forming a new government after walking out of the 3-party grand alliance which also included the Congress.
As suspense mounted over Kumar's next step, BJP quickly seized upon the opportunity to reunite with its old ally, with Prime Minister Narendra Modi praising Kumar for "joining the fight against corruption", saying the entire nation supports his honesty.
Also Read
The move was seen as an effort to reach out to JD(U), which had ended its 17-year association with BJP in 2013 after Modi was nominated the saffron party's campaign committee chief for 2014 Lok Sabha elections.
Legislators of NDA constituents and JD(U) will meet to elect Nitish as their leader, Modi said, without elaborating on when it would happen. He said the governor will be apprised of the decision soon.
In the 243-member Bihar Assembly, JD(U) has 71 MLAs and the BJP 53. The two parties together have 124 MLAs, marginally ahead of the half-way mark. Besides, they have the support of NDA allies LJP (02) and RLSP (02).
"1.25 crore people are welcoming and supporting his honesty," Modi said in a series of tweets after Kumar announced his resignation.
"For the bright future of the country, and especially Bihar, it is the need of the hour to rise above political differences and join the fight against corruption," Modi said.
Kumar responded with a quick tweet saying," I thank the prime minister from the core of my heart for praising my decision (of quitting)."
Earlier, Kumar, when asked about the chances of his forming a government with BJP's support, said,"Whatever will be in the interest of Bihar will be done. Wait for the future to unfold. Whatever had to happen has happened. Now see what happens next."
"I tried to work it out....I did not ask for anybody's resignation...I just asked Tejashwi to explain the charges of corruption," he said.
After the CM made the announcement, Lalu broached the idea of forming an alternative government without Kumar or Tejashwi heading it. He said since the people's mandate to the grand alliance was for a five-year term, it should be respected.
Tensions simmered between the two alliance partners ever since the CBI registered a case against Lalu Prasad, his wife and former chief minister Rabri devi and son Tejashwi in a land-for-hotels case.
Lalu gave a new twist to Kumar's resignation, saying a pending case against him and not the differences over corruption charges against Tejashwi was at the root the the JD(U) leader's "resignation drama".
In the 1991 Lok Sabha polls, a man named Sitaram Singh was killed at a polling station in Pandarak and Nitish Kumar is among the accused. He had made a mention of the case in the affidavit he filed while contesting the Legislative Council election, Lalu told a press conference.
"Nitish knew that he was soon going to be hauled up by the court and will have to quit in any case. He made the Tejashwi issue a ruse to exit before that happens," the RJD boss claimed.
He slammed Kumar for seeking explanation from Tejashwi over graft charges against him, saying "We will give the documents to CBI. Who are they to ask for it? Has Tejashwi engaged in any act of corruption as a minister in Bihar?"
Replying to a question, Lalu said he had not sacrificed the grand alliance government for "love of his son".
"We were the largest party in the grand alliance. Tejashwi got the post of the deputy chief minister. We had the mandate of the people," he said.
Meanwhile, Union Minister J P Nadda and BJP general secretary Anil Jain were being rushed to Patna as observers for a meeting of the party legislators.
Disclaimer: No Business Standard Journalist was involved in creation of this content