From the news stories I have been reading – I think one of the biggest reasons for BJP loss was – Prashant Kishore defecting to Nitish Kumar’s side. He has been the brain behind LS elections and other state elections for Modi. He is politically agnostic, and hence, just wanted a cabinet post to provide in national policy matters after the victory of LS elections. BJP being an ideological party, could not give cabinet posts to anybody from outside the party. This pissed him off and he went to Nitish’s side to teach BJP/Modi/Shah a lesson. Whatever retorts Nitish came up with during the campaign were actually coming from this guy – Prashant Kishore.
Apparaently, Prashant Kishore gave a presentation to Gandhi family to provide service of professional campaign management before 2014 elections, but, Gandhi family didn’t buy into him. And then he came to Modi – whom he impressed to get the service contract for campaign management for LS elections.
He was the reason why BJP got a very high seat-vote-share ratio in LS elections and why JDU+ got a high seat-to-vote-share ratio in Bihar elections. In Bihar, BJP got ~35% vote share, but, couldn’t convert them to seats.
These stories, if true, means, he can pick any Tom, Dick or Pappu and make him/her a chief/prime minister. I know Modi’s work is much important to have swayed by one person, but, it seems reasonable that a professional campaign manger can win you elections. My worry though, is that, so far India has only one such super-successful campaign manager who doesn’t know which party represents the “Greater Good”.