The Sena said in an editorial that politics today was "no longer about morals and ideals" and added that Prime Minister Narendra Modi and BJP chief Amit Shah had "snatched away" the opposition's prime ministerial face.
"Amit Shah had earlier said if Nitish Kumar won, Pakistan would celebrate. So is Pakistan celebrating now," it asked in the editorial in the Sena mouthpiece, 'Saamana'.
It said, "It seems that the BJP itself has made Pakistan happy by collaborating with Nitish".
The NDA has got its "old friend" back, it said, but pointed out that Kumar had "splashed a lot of muck" on Modi when he left the NDA.
"Has that muck been washed off now," asked the Sena, a constituent of the BJP-led NDA government at the Centre and in Maharashtra.
"In just two years, after Modi kept on with his winning spree, Nitish Kumar's conscience once again made him join the NDA fold. Politics is no more about ideals and morals," it said.
The BJP formed a government in Manipur and in Goa despite not having a majority, it said.
"The BJP should ask its conscience if this would have been possible if the party did not have its government in Delhi," the Sena said.
It said the BJP should "immediately ask" Nitish Kumar to clarify his views on violence by gau rakshaks (cow vigilantes).
"Nitish Kumar was the prime ministerial face of the opposition parties. Modi and Amit Shah have snatched that face away," the Sena added.