Prashant Kishor of the Jan Suraaj Party wrested the Bankipur assembly seat in Bihar from the BJP, reducing the ruling party's vote share to a historic low of 34 per cent.
Congress leader Kuwar Ghanshyam Singh retained the Datia assembly constituency in Madhya Pradesh, dealing another significant blow to the BJP in its traditional stronghold.
The BJP's defeat in Bankipur was fueled by upper-caste and Kurmi resentment following the replacement of Nitish Kumar with Samrat Choudhary as Bihar Chief Minister.