Here are 10 big developments on this story:
The intended return to power of Mr Kumar has fissured his party, the Janata Dal (United) or JD(U), which runs a minority government in Bihar.
Today will see key meetings being held by both leaders. Mr Manjhi has called a cabinet meeting. Mr Kumar and JD(U) chief Sharad Yadav have summoned a session of all lawmakers from the party.
At that gathering, the JD(U) is expected to formally announce that it's time for Mr Kumar to take over as Chief Minister; the state votes later this year, and the party wants Mr Kumar to be the face of its campaign.
Mr Manjhi had dismissed the meeting as "illegal" because he says as Chief Minister, only he is empowered to call a gathering of the party's representatives in the state legislature.
At the cabinet meeting he has scheduled, he may formally step down, say sources.
Mr Manjhi had last night written to the Governor asking for the removal of two ministers seen as loyal to Mr Kumar.
Sources say that Mr Yadav, the JD(U) chief, invited both leaders to a meeting and brokered peace between then.
Mr Kumar resigned as leader of the government last year, accepting responsibility for the JD(U)'s abysmal performance in the national election.
Mr Manjhi has, in recent months, signalled that if he were forced out of office, crossing over to the BJP is a viable option. Others in his party could follow. The BJP, powered by the Prime Minister's campaigns, has won elections in other states, and many in the JD(U) take this as a sign of things to come for Bihar.
To counter the BJP - and to remain in power - the JD(U) is aligned formally with Lalu Prasad Yadav, with whom it was once entrenched in hostility. Lalu's RJD props up the minority state government.
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