After its stupendous victory in West Bengal, the Trinamool Congress appears to be on a mission mode - to weaken the Congress. 

West Bengal Chief Minister Mamata Banerjee's party is heavily poaching Congress leaders from across the country to expand its base and emerge as a national party. 

But its move in Meghalaya takes the cake. On Wednesday, former Meghalaya Chief Minister Mukul Sangma, along with 12 of the 17 Congress legislators in the state, joined the Trinamool Congress. 

This is undoubtedly a coup of sorts given that the move has enabled the Trinamool Congress to become the main opposition party in the northeastern state. 

Earlier in the day, Meghalaya Congress legislators wrote to assembly speaker Metbah Lyngdoh and briefed him about the development.

The Congress now has only five legislators. 

The move came at a time when Banerjee is in Delhi and had spoken of her plans for a united opposition.

Sangma had earlier visited Kolkata and met top Trinamool Congress leaders there and his closeness to political strategist Prashant Kishor is well-known. The two had also met during Sangma's visit to Kolkata. 

While Sangma had initially categorically stated that he is not quitting the Congress, his differences with the party leadership had increased and it had become untenable for him to stay out.

He had met former Congress President Rahul Gandhi last month following the escalation of tensions between him and state party chief Vincent H Pala.

The joining came a day after former Congress leaders Kirti Azad and Ashok Tanwar joined the Trinamool Congress in Delhi on Tuesday in presence of Banerjee.

The Trinamool Congress is giving jitters to the Congress in Goa and has already occupied the space of the main opposition party in Tripura.

The Congress has accused Banerjee of working at the behest of the BJP.

West Bengal Congress President Adhir Ranjan Chowdhury alleged that the Trinamool Congress and Banerjee are acting as agents of the BJP on a mission to destroy the opposition unity and his party.

"Everybody knows that only Congress can fight the BJP. So they have assigned the job to finish the Congress to the Trinamool Congress."