Manvendra Singh accused Prime Minister Narendra Modi of doing nothing for Rajasthan.
A day after he joined the Congress, former union minister Jaswant Singh's son Manvendra Singh has accused the BJP of "insulting" his father.
"People of Rajasthan will take revenge from the BJP for insulting Rajput leader Jaswant Singh in the December 7 assembly election," Manvendra Singh said today.
Mr Singh, who joined the Congress on Wednesday, said that quitting BJP wasn't easy for him.
"It was not easy for me to quit the BJP as it was my family. But when no one heard me within the family and a friend (Rahul Gandhi) heard me, it was then that I took this step," he said.
Manvendra Singh was the BJP MP from Barmer in Rajasthan from 2004 to 2009.
"The people of Rajasthan, especially from Barmer, Jalaur, Jaisalmer and Jodhpur will take revenge for the insult caused to my father Jaswant Singh when he was denied the party ticket and expelled (from the BJP)," he told PTI.
BJP veteran Jaswant Singh was denied the party ticket in the 2014 Lok Sabha elections but he contested as an independent candidate from Barmer and lost to Sona Ram, who came into the BJP from the Congress. He was later expelled from the BJP for contesting the election against the party's official candidate.
"After (former Prime Minister) Atal Bihari Vajpayee left, the BJP's traditional values are no longer there. I feel the decision taken by me (to quit the party and join the Congress) has Atal ji's blessings," he said.
He accused Prime Minister Narendra Modi of doing nothing for Rajasthan and said that the people will throw out the Vasundhara Raje-led government in the state.
"Joining the Congress was not just my personal decision, it was also a collective decision taken by my supporters who are fighting for their self-respect," he said.
On being asked if Congress president Rahul Gandhi was capable of leading the country, Manvendra Singh said "In a democracy, a leader has to possess humanity. If one does not possess that, one cannot feel the pain of the poor...Rahul ji is a repository of humanity. I have seen him very closely. Very few leaders possess such deep humanity," he said.
The 200 assembly seats in Rajasthan will on December 7 and the results will be declared on December 11.