Former student leader Kanhaiya Kumar, who joined the Congress this week, on Friday stood firmly in defence of his new party's leadership that has faced searing criticism from within in the wake of a series of crises in states that it governs and an exodus of prominent leaders. "Criticism of the Congress leadership helps the BJP... Everybody understands that when the country's biggest opposition party is Congress, the more successful Congress will be, the bigger the defeat BJP will face," he told NDTV in an interview.