How did Bihar go from a 2020 cliff-hanger to a 2025 landslide?

THe 2020 gathering elections were a photo destination in Bihar and both john major alliances ended up with almost the same voter turnout portion out with a difference of just 0.03% in the votes polled between them. This time, the National Democratic Alliance (NDA) has around a 10 percentage points lead in terms of vote share vis-à-vis the Mahagathbandhan (MGB) or Grand Alliance. As is often the case in the first-past-the-post system, the seat share difference between the two alliances has increased even more: a massive 68.7 percentage point lead for the NDA compared to just six percentage points in 2020. What really happened? Here is a breakdown of the electoral math, as it changed between the 2020 and 2025 elections in Bihar.MGB retained its popular support, but NDA increased it significantlyWhile MGB’s vote share is almost identical between 2020 and 2025 (37.23% and 37.9%), NDA’s has increased from 37.26% to 46.6%. Where did NDA get its additional support from in these elections?Around five percentage points of extra vote share has come from the two main constituents, namely, the Bharatiya Janata Party (BJP) and Janata Dal (United) or JD(U). That this has happened despite the two parties contesting a lower number of seats this time (202) than in 2020 (225) underlines the scale of their achievement. Among the two, it is the JD(U) which has increased its vote share more, as it was far behind the BJP last time (more on this later).Most of the rest of the extra vote share has come from the Lok Janshakti Party (Ram Vilas) or LJP, which contested outside the NDA last time and largely hurt the JD(U) by playing spoiler. LJP’s vote share has remained largely unchanged in the 2020 and 2025 elections: 5.7% and 5% respectively.Also Read | After stunning defeat in Bihar, doubts rise on Congress' INDIA leadershipTo be sure, the NDA also lost one constituent – the Vikassheel Insaan Party (VSIP) – to the MGB alliance in this election, which had 1.5% votes in 2020. This loss was made up by Upendra Kushwaha’s Rashtriya Lok Morcha (RLM) joining the NDA in this election instead of contesting in the AIMIM-led alliance in 2020 and Jitan Ram Manjhi-led Hindustani Awami Morcha (Secular) also increasing its vote share marginally. (See Chart 1)NDA’s higher vote share increased the winning threshold in Bihar this timeThe consolidation of non-MGB voters behind the NDA meant that what was a winnable performance for most MGB candidates in 2020 was not good enough this time. The average winning candidate has polled 47.8% votes this time which is the highest median victory margin for a candidate in the state since the 1977 elections in the state. In fact, if one were to arrange winning candidates by their vote share in the 2025 elections, 71.4% of the MGB’s winning candidates have polled a lower than median vote share. (See Chart 2A and 2B)And there were very few spoilers to help MGB victoriesSpoilers were a big factor in MGB’s victories in the 2020 assembly election. The MGB won 65 seats where the party finishing third had vote share more than the victory margin thereby theoretically playing spoiler for the party finishing second. This number has decreased to just 23 in the 2025 election.This drastic decline has happened because two NDA constituents – Chirag Paswan’s LJP and Upendra Kushwaha’s RLM, known in 2020 as Rashtriya Lok Samta Party (RLSP) – contested outside the NDA in 2020.These two parties alone contributed 40 of the 65 seats (30 by the LJP and 10 by the RLSP) that the MGB won because of spoilers, 28 of which were lost by the JD(U) alone. To be sure, with JD(U) pitted against the LJP in the 2020 election, even the JD(U) ended up helping the MGB win in nine seats in 2020 by playing spoiler, four of which were lost by the LJP.NDA victories because of spoilers have also fallen, but that is also because in 68 out of the 202 ACs they have won with a vote share of more than 50% which makes spoilers redundant. (See Chart 3)The resurrection of JD(U) against RJD in 2025As the discussion so far suggests, most of the boost to the NDA’s fortunes has happened because of an improvement in the JD(U)’s performance as a result of the LJP coming back in the NDA fold instead of hurting the JD(U). A large part of this improvement is focussed in direct contests with the Rashtriya Janata Dal (RJD). There were 61 seats in 2020 (out of 115 and 144 that the JD(U) and RJD contested overall) where only these two parties finished in the top two positions. The RJD won 40 of these 61 contests. This table has flipped in favour of the JD(U) in this election.The JD(U) and the RJD were again in a direct contest in similar number of seats (59) this time out of the 101 and 143 seats they contested overall.The JD(U) has won 50 of these contests. This is not very different from what happened in 2010 when the NDA ended up with an almost similar seat tally. (See Chart 4)