Mritunjay Tiwari, the national spokesperson of the RJD, said: "Nitish Kumar of the JD(U) has the longest parliamentary life than any other leader. He is an experienced leader who knows how to govern the country. He has a clean political and socialist image and other leaders are nowhere near to him when we talk about quality leadership."

"The parliamentary life of current Prime Minister Narendra Modi is less than Nitish Kumar. Besides, the latter has a socialist image which makes voters comfortable. Narendra Modi on the other hand has done nothing in the last 8 years other than communal politics. Moreover, the central government has many anti people policies which have created anti incumbency against the BJP. The Narendra Modi government has failed on every count including the economy. The prices of commodities are increasing and the income of the people is decreasing. The life of the common people has become hard and such a factor can act against Narendra Modi," Tiwari said.

"As far as the opposition parties are concerned, everyone is in favour of a 'BJP Mukt Bharat'. The primary objective of every opposition party is to remove the BJP government from the Centre and not who would be the PM candidate of the opposition parties. Nitish Kumar himself has said that he is not the prime ministerial candidate at present. He also said that all opposition parties will sit together to decide the name of the prime ministerial candidate of the opposition parties to challenge Narendra Modi," Tiwari said.

The opposition leaders know well the political style of the BJP. It believes in the character assassination of leaders who are in the opposition. They were with Rahul Gandhi and he was given the name Pappu. The only aim was to defame Rahul Gandhi and demoralize him. Rahul is still standing firm and taking on the BJP in his own style, they said.

"For Nitish Kumar, he has not been involved in any scam or has any serious allegation or any baggage of corruption. Hence, it would not be easy for the BJP to target him. Moreover, he is a Hindi heartland leader capable of counter attacking Narendra Modi in his own style. If we remember, Narendra Modi during the 2015 Vidhan Sabha election commented on his DNA. Nitish Kumar immediately responded with Badka Jhutha Party for BJP," said Chitranjan Gagan, another RJD leader and spokesperson.

As far as the RJD is concerned, it has been out of power for 15 years in Bihar. Moreover the party's national president Lalu Prasad may not have national ambitions as he is ill and suffering from multiple diseases. The second big leader of the RJD is Tejashwi Yadav and he is focusing on Bihar.

In Uttar Pradesh, the Samajwadi Party's Akhilesh Yadav is out of power. Hence, he is trying to consolidate his position in the state rather than thinking of national politics. His father and a big socialist face Mulayam Singh Yadav is also ill and not in a position to contest elections. Trinamool Congress supremo and West Bengal chief minister Mamata Benerjee is a possible challenger to the Narendra Modi government but her acceptance in the Hindi heartland is a million dollar question.

Delhi chief minister Arvind Kejriwal could be another challenger to Narendra Modi but his fate will be decided only after the AAP's performance in the Gujarat and Himachal Pradesh assembly elections. If he manages to defeat the BJP in Gujarat, his chances as the opposition's prime ministerial candidate become brighter.

For the Congress, Rahul Gandhi and Sonia Gandhi are doing national politics and hence leaders like Ashok Gehlot and Raman Singh are not in the race. For leaders like KCR, MK Stalin and Sharad Power, it would not be easy to challenge Narendra Modi who is a very good speaker in Hindi.

"Challenging Narendra Modi in his own style would be one of the key aspects for the opposition parties where Nitish Kumar is far more experienced than anyone else. He is also a supporter of RJD and it means its 79 MLAs and 12 MLCs are also favouring Nitish Kumar who is having 45 MLAs in Bihar and 17 Lok Sabha MPs," said a RJD leader requested not to be named.