The BJP, politically isolated in Bihar, is holding a brainstorming session this evening where the party's senior-most leaders are in favour of focussing on the upper castes and finding a face that can challenge Nitish Kumar, sources said. The meet -- led by Union home minister Amit Shah and party chief JP Nadda -- are also likely to agree to a series of rallies in the state with the "pol khol (unmask) Nitish Kumar" theme, sources said.