By-elections to the Araria Lok Sabha seat and Bhabua and Jehanabad assembly constituencies, vacated due to the deaths of sitting lawmakers, will also gauge the political acumen of opposition leader Tejashwi Yadav, who has led the campaign in as his father and RJD chief Lalu Prasad is in jail in a corruption case.
In Araria, a seat that fell vacant after the death of RJD lawmaker Mohd Taslimuddin, the party has fielded his son Sarfaraz Alam, looking to capitalise on Muslim and Yadav voters who make up a big chunk of the electorate. Mr Alam is locked in a direct contest with the BJP's Pradip Singh who came second in the 2014 general elections but had won the seat in 2009.
While Tejashwi Yadav has addressed several meetings in Araria over three days, Nitish Kumar has addressed two rallies.
"I am confident of victory this time. My defeat in 2014 was not a result of Taslimuddin's popularity. We suffered as votes of the Mahadalits and the Extremely Backward Classes (EBCs) had split between the BJP and the JD(U)," Mr Singh said.
In Bhabua that was held by BJP's Anand Bhushan Pandey, the party has fielded his widow Rinki Rani Pandey. On a seat that has a sizeable population of Dalit voters, the Congress has put up Shambhu Patel, banking on the popularity of former Lok Sabha speaker and Dalit leader Meira Kumar, who has earlier represented Sasaram, the parliamentary seat of which Bhabua is an assembly segment.
In Jehanabad, where the assembly by-elections are taking place due to the death of RJD lawmaker Mundrika Singh Yadav, the RJD has fielded his son Uday Yadav. He is in a direct battle with JD(U)'s Abhiram Sharma who had won the seat in 2010 when his party was an ally of the BJP.