New Delhi: The Bharatiya Janata Party's (BJP) 4-1 defeat in the Karnataka by-elections has further lengthened the list of the party's reverses in more than 20 by-polls spread across Uttar Pradesh, Bihar, Jharkhand, West Bengal, Kerala, Punjab, Maharashtra and elsewhere. The winners include the Samajwadi Party, the Rashtriya Janata Dal, the Rashtriya Lok Dal, the Congress, the Trinamool Congress, the Nationalist Congress Party and the Jharkhand Mukti Morcha. In all these seats, what has led to the BJP's defeat is a one-to-one contest against it by a combined opposition. It is obvious that if such unity is achieved in the forthcoming elections, the BJP's chances of success are minimal, notwithstanding its claims about booth-management tactics of party president Amit Shah and the party's seemingly huge resources.

The idea of a one-to-one contest against the BJP was first floated by West Bengal Chief Minister Mamata Banerjee, but she appears to have taken a back seat lately after the collapse of a federal front proposed by her in the company of the Telangana Chief Minister K. Chandrashekhar Rao, who has now distanced himself from taking on the BJP along with other "secular" parties.

Instead, his place has been taken by the Andhra Pradesh Chief Minister, Chandrababu Naidu, who has been contacting various leaders in the anti-BJP camp -- H.D. Deve Gowda, H.D. Kumaraswamy, Rahul Gandhi and Sharad Pawar -- to stitch together an alliance against the Narendra Modi government.

There is little doubt that the success of the Janata Dal (Secular)-Congress combine in Karnataka will give a boost to Naidu's efforts, not least because the earlier signs of tension between the two parties had led to doubts about their electoral success.

However, the large margins of their victories, especially in the supposed BJP stronghold of Bellary, have shown a popular acceptance of the ruling alliance, encouraging Chief Minister Kumaraswamy to predict that the combine will win all the 28 parliamentary seats in the state in 2019.

For the secular camp, what must have been most reassuring about the Karnataka outcome was the clear indication about the durability of the ruling alliance at a time when the BJP continues to harp on the "khichdi" or hodge-podge nature of the opposition formations and their hedging on the question of who will be the leader at the national level.

There is no definite answer to this question as yet with the opposition leaders saying that they will cross the bridge when they come to it. But this indecisiveness is bound to remain a potent weapon in the BJP's armoury when it comes to needling its opponents.

It is also clear that the cohesion of the Karnataka alliance is not reflected in a state like Madhya Pradesh, where the Congress appears to be as much preoccupied with keeping peace among the three bigwigs of the party -- Kamal Nath, Digvijay Singh and Jyotiraditya Scindia -- as in fighting the BJP.

For the Congress, it is an acid test in Madhya Pradesh, for if it cannot take advantage of the inevitable anti-incumbency sentiments against chief minister Shivraj Singh Chauhan after three successive terms, then the party would have only exposed its own fatal weaknesses.

As it is, the Congress failed to bring the Bahujan Samaj Party (BSP) on board in Madhya Pradesh and could not dissuade the BSP supremo, Mayawati, from aligning with the breakaway Congress leader, Ajit Jogi, in Chhattisgarh. As a result, the Congress has been left with its only best hope in Rajasthan whereas it was earlier expected to have an easy run in all the three states.

Notwithstanding the series of by-election successes, the opposition's expectations of making an impact in 2019 will depend on the outcome in the three states and on whether the tie-up between the Samajwadi Party and the BSP remains intact in U.P.

By breaking away from the Congress in Madhya Pradesh, Chhattisgarh and Rajasthan, Mayawati has raised doubts about her commitment to the idea of opposition unity. Although she played a proactive role last May to bring the Congress and her ally, the Janata Dal (Secular), together when the Karnataka assembly elections produced a hung verdict, she has remained silent about the latest by-election results.

Instead, she is apparently concerned about the bonhomie between the Congress and the Bhim Army leader of the Dalits, Chandrashekhar Azad "Ravan". It is possible that the Congress-BSP negotiations failed in the three states which are going to the polls this month because of Mayawati's fear of the Congress poaching on her territory by wooing the Dalits and rebuilding its old Brahmin-Muslim-Harijan base, which paid handsome electoral dividends for the party in the past.

Clearly, Naidu's unity efforts will have to focus much more on Mayawati than on any other leader, nearly all of whom can be said to have already climbed on board the opposition bandwagon.