Thiruvananthapuram: The Congress' Kerala unit termed the resignation of Karnataka Chief Minister B.S. Yeddyurappa, ahead of his trust vote in the assembly, as the biggest setback for Prime Minister Narendra Modi and his BJP.

Leader of Opposition in the Assembly Ramesh Chennithala said this is the biggest failure of Modi and BJP President Amit Shah who tried to manipulate democracy.

"They tried to promote horse trading and it ended as a big failure. Equally responsible for what happened in Karnataka is the role played by Governor Vajubhai Vala, who has no other option but quit. They tried their best to subvert democratic principles and failed badly and in the end democracy came out a winner," he said.

State Congress President M.M.Hassan said the manner in which the BJP tried to manipulate democratic traditions led to a huge setback for them.

"A case should be registered against Yeddyurappa who tried to cling on to power through horse trading, for which evidence are now out. Likewise the Governor should be booted out," he demanded.

Former Congress president V.M.Sudheeran said this resignation will go down as the most shameful one in the history of Indian democracy as both Modi and Shah used both power and money power to do their best for their party leader, while the Governor has proved he is unfit for that post.

Yeddyurappa resigned on Saturday before facing a crucial trust vote in the Karnataka Assembly with numbers stacked against the BJP in the newly elected House, bringing an end to a political thriller that began after May 12 elections threw up a hung verdict.