Months of simmering tensions between the BJP and JD (U) over Narendra Modi's rising profile blew up into a full-scale war on Sunday, with the junior ally attacking the Gujarat chief minister and the senior partner telling it bluntly to desist from it.
Addressing his party's national meet on Sunday, senior Janata Dal (United) leader and Bihar chief minister Nitish Kumar questioned Modi's secular credentials.
His party also set a year-end deadline for the BJP to choose an "inclusive figure" with impeccable secular credentials for the prime minister's post.
Within hours of Kumar's stinging but covert attack, the BJP rejected all "unfounded inferences against Shri Narendra Modi" and asked allies not to dilute the anti-UPA pitch by attacking "our chief ministers".
There has been a growing chorus within the BJP for naming the Gujarat CM as the party's PM candidate for the next year's general elections.
Recently, he was promoted to its highest decision-making body that will play a vital role during the polls.
Kumar, who on many occasions has made his reservation about his Gujarat counterpart known, didn't mention Modi by name but the BJP got the message loud and clear and was not happy about it.
The Bihar CM's attack took the BJP leadership by surprise as a night earlier party chief Rajnath Singh told him that it was too early to talk about a PM candidate.
The party was forced to hit back when Kumar launched an all-out offensive against Modi even after the meeting.
Only a leader who could take everyone along should lead the country - something which required the inclusive vision of Atal Behari Vajpayee, Kumar said on Sunday.
He even referred to the former PM's "follow rajdharma" statement issued in the aftermath of the communal violence that ravaged Gujarat in 2002.
"We'll want to walk on… the path of harmony, love, peace and respect for all. For that, you'll have to sometimes wear a skull cap and sometimes apply a tikka," he said.
It was a veiled reference to Modi refusing to wear a skull cap offered by a Muslim during a chain-fast last year.
"To say that Modi had engineered the riots or took the side of one community cannot be expected from any chief minister," the BJP chief said during an interview televised in the evening.
Kumar even took on Modi on his favourite theme - the Gujarat growth story - wondering how development could coexist with malnourishment and water crisis.
In Bihar, development included backward castes, the poor, Dalits and women, said Kumar, adding he was not in the race for PM.
Though Bihar didn't have a business tradition, it had a rich heritage and a tradition of learning, said Kumar.
Modi's critics compare his Gujarat success with Kumar's Bihar turnaround and even see the JD (U) leader as a potential PM candidate for the NDA. Modi vs Nitish: two CMs and their unease with each other
Earlier in the day, Sharad Yadav, who was elected the party chief for a third term time, pitched for the alliance to continue. He also asked party leaders not to speak out of turn.
"We have nothing to do with any particular person... This fight is only for principles... We should avoid taking names...," he said.