Here are 10 big developments in this story:
On Friday, Mr Manjhi will need 117 votes to remain Chief Minister. If the BJP in Bihar decides to back him, he will get the support of the party's 87 lawmakers. The BJP is expected to formally indicate its plans by 6 pm today.
Mr Manjhi has been expelled from the Janata Dal (United) or JD (U), which governs Bihar, and which decided earlier this month that he should step down to allow the return of Nitish Kumar as Chief Minister.
Mr Manjhi rebelled against that decision. He has 12 lawmakers from the JD(U) in his camp. So even with the support of the BJP, he is poorly placed to win the trust vote tomorrow.
Nitish Kumar, on the other hand, should be able to accrue 120 votes, which would make him Chief Minister.
Despite numbers not adding up, Mr Manjhi has maintained that he has the support to continue as chief minister. He has called a cabinet meeting this evening to demonstrate that it is work as usual for the Bihar government.
Mr Manjhi, 70, is a Mahadalit - a caste whose support is vital for political parties. The BJP wants to project itself as a party that backed a Mahadalit leader against the odds because of its commitment to one of the state's poorest castes.
In a build-up to what is now seen as a Nitish Kumar vs BJP battle, the Assembly Speaker has granted the status of principal opposition to the JD (U). An angry BJP, which was the main opposition till now, staged a noisy protest this morning.
Bihar votes for its next government later this year. The JD (U) wants Mr Kumar, 63, to be the face of its campaign for the election. The party has allied with Lalu Prasad Yadav's Rashtriya Janata Dal or RJD to take on the BJP.
The BJP and the JD (U) aborted a lengthy alliance at the insistence of Mr Kumar ahead of the national election. He was opposed to the BJP's decision to select his arch-rival, then Gujarat Chief Minister Narendra Modi, as its prime ministerial candidate.
Mr Kumar erred gravely. His party won just two seats in the national election, and he resigned, accepting responsibility for the colossal wipeout. He alleges that Mr Manjhi's rebellion has been scripted by the BJP to undermine his position.
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