The JD(U), led by Kumar, had contested and won the 2015 Bihar Assembly polls with the RJD and the Congress, defeating the BJP-led NDA.
"The grand alliance was formed to bring secular forces together, to fight the dictatorial attitude of the BJP, its attitude of killing democracy," Kharge told reporters outside Parliament.
But those who had sought votes in the name of secularism, had embraced the BJP, he said.
In an apparent reference to the ostensible reason being cited for Kumar's decision to quit the government -- corruption charges against his then deputy Tejashwi Yadav of the RJD -- Kharge said the JD(U) chief was "fully aware" of the constituents of the alliance.
"You formed the government in Bihar fully aware of how the grand alliance partners are. You should not have broken the alliance in such a case," he added.
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