Or, specifically, the fact that Modi belongs to the "ati-pichhda (Extremely Backward)" class ' believed to be a Nitish vote bank.
The EBC category includes more than 100 castes dispersed thinly across the state but which form a considerable chunk together. They are believed to be numerically much more than the Yadav community, considered the RJD's core support base. The EBCs have been staunch Nitish backers since his government in its first tenure provided them reservation in panchayats.
Trust it on the entrenched nature of identity politics in Bihar that BJP workers sincerely believe that Modi ' despite his carefully crafted image of a development-oriented leader who is above caste identities ' being an EBC can help them poach on JD(U) territory.
"Don't forget that Modi belongs to a backward class. That too, from what we understand, an EBC," said a BJP district president. "Isliye, ati-pichhda varg puri tarah se BJP se nahin jayega, Modi OBC hain isliye bahut sara hamare saath aayega, aap dekhiyega (That's why, in case of a split, we won't lose the entire EBC vote. Since Modi is OBC, we will get a lot of their votes, you'll see)."
This reasoning was offered by several BJP district presidents to The Indian Express during its tour of Bihar when asked whether the BJP stood to lose the EBC vote in a parting of ways with the JD(U). Several central office-bearers of the party in Delhi also privately confide that Modi's caste could be a stealth weapon in the Hindi heartland that thrives on identity politics.
One Bihar party leader went one step further to insist: "Nitish is afraid of Narendra Modi because it is for the first time a national party has projected an OBC leader as the prime ministerial candidate. In fact, this is rattling all the leaders championing social justice."
However, while another BJP district president claimed that the signficance of Modi's caste is also trickling down to the electorate, that may be a bit far-fetched.
As a backward community member from Sarisab village in Madhubani Lok Sabha constituency noted, Bihar has two strong backward class leaders in the form of Nitish and Lalu Prasad Yadav already. "Agar BJP ko in donon se pichhda vote kheenchna hai, toh unhe chilla-chilla kar prachar karna padega ki Modi kis jaati ke hain. Yeh chhup kar ke, voter ke kaan mein bolkar batane se kaam nahin chalega (If the BJP wants to capture the backward vote from them, it will have to shout Modi's caste from the rooftops. This hush-hush whispering in voters' ears will be of no use)," observes Mahendra Sah. "I don't think the BJP can ever assert his caste so publicly," he adds presciently.
Asked about this, a state BJP leader at the party headquarters at Patna gave the example of former PM Atal Behari Vajpayee. "Vajpayeeji never had to say that he was a Brahmin. All he had to do was note at a Kanpur meeting that people alleged that Pandit Shankar Dayal Sharma had gone out of his way to swear him in as PM, and that there was no caste motivation in it. The message reached where it was meant to reach," the office-bearer said.
However, if the BJP is hoping for some EBC support courtesy the Modi factor, it could also lose own some of its own upper caste vote to Nitish. While they are largely Modi backers, there appears to be enough support for the Bihar CM to make inroads.
"Choonki upper-caste padha-likha hai, isliye log kah rahe hain ki wo Modi ko PM banana chahta hai. Lekin padhe-likhe aur chaalu hone mein antar hai (Since upper castes are educated, people say they want Modi as PM. But being educated is one thing and being cunning is another)," says Acharya Arvind Shastri, a priest in Kathra village of Darbhanga Lok Sabha constituency. "Upper castes are also cunning and they realise that to stop Lalu in Bihar, they need the JD(U). Anyway, Nitish too is bringing development. His development we have seen; as for Modi's, we have only heard of it."
Paramhans Bhagat, a Brahmin at Sheohar, also underlines that the upper castes can't forget Nitish's role in ousting Lalu.
However, such upper caste sentiments do not appear deep enough across many Lok Sabha constituencies yet, indicating that Nitish has to put in extra effort if he wants to turn his developmental record and dismantling of lawlessness into solid support for him in case of a split with the BJP.
The deciding factor could well then be Modi's polarising potential. Admits Magandev Prasad, member of an EBC Turha community in Sheohar, who is associated with the JD(U): "If the elections become a Hindu-Muslim issue, some EBCs may get swayed in the Hindu wave."