As much as the internal strife within the party can be blamed for the fall of Congress in Assam and many other states in India, a handful of external factors also led to its downfall. Failure to take along all constituents of its voter base despite having good relations with all of them proved to be detrimental as the BJP was quick to cash in on the gaps. Whether it was the Muslims, tea garden workers or the various Scheduled Tribes in Assam, the Congress no longer has a consolidated voter base to fall back upon.
Abandoned, Scheduled Tribes walk out of Congress hold
"Everyone knows why we lost our dominance in Assam after being in power for 15 years. One has to admit that various major groups of Congress supporters were alienated by the party from time to time because of the mistakes of Congress state leadership making BJP the biggest beneficiary. Take the example of the support enjoyed by Congress among the Bodo population. Congress had an alliance with the Bodo People's Front but the alliance was abandoned suddenly without any backup plan. This only led to the mobilisation of most tribal outfits into an anti-Congress mode," said senior Congress leader Kirip Chaliha.
 
Former Congress president Rahul Gandhi with Assam state Congress president Ripun Bora. AssamINC's Facebook page
Significantly, most of the Scheduled Tribes got their autonomous council status when the Congress was in power in the state. The Karbi Anglong Autonomous District Council came into being on 1 April, 1996 when the Congress was in power under then chief minister Hiteswar Saikia. The Dima Hasao Autonomous District Council, which was earlier known as North Cachar Hills Autonomous Council, came into existence on 2 February, 1970. Bimala Prasad Chaliha from the Congress was the chief minister then.
Both the Dima Hasao Autonomous District Council and Karbi Anglong Autonomous District Council enjoy their autonomy under the Sixth-Schedule of the Constitution.
The Bodoland Autonomous Council was created under the Bodoland Council Act of Assam, amended on 8 April, 1993 and it received the assent of the president on 3 May, 1993. It is also covered by the Sixth Schedule of the Indian Constitution with Saikia at the helm of affairs in Assam.
The Rabha Hasong Autonomous Council was formed under the Rabha Hasong Autonomous Council Act of 1995. In 1995, Saikia was the chief minister of Assam. It remains same for the Mising Autonomous Council, which was established under the Mising Autonomous Council Act, 1995 passed by Assam Legislative Assembly with its headquarters in Gogamukh. Similarly, the Lalung (Tiwa) Autonomous Council Act, 1995 was enacted by the state legislature and an interim Lalung (Tiwa) Autonomous Council was created.
The Deori Autonomous Council was established under the Deori Autonomous Council Act, 2005 and passed by Assam Legislative Assembly with its headquarters at Bhimbar Nagar. The Assam government passed the Thengal Kachari Autonomous Council on 12 August 2005 while the Sonowal Kachari Autonomous Council came into existence on 8 May, 2005 when Tarun Gogoi was the chief minister. The Rabha Hasong Autonomous Council, Mising Autonomous Council, Tiwa Autonomous Council, Deori Autonomous Council, Thengal Kachari Autonomous Council, Sonowal Kachari Autonomous Council are all Statutory Autonomous Councils constituted under State Act.
"Although the Muslim and tea garden community factor always got the limelight, there was a huge Scheduled Tribe voter base of the Congress which was silently voting for the party. They have always remained the deciding factor but mostly underrated. However, once Sarbananda Sonowal's image got a boost as the chief minister of the state, his government conducted rounds of talks with all the ethnic organisations and created a deep understanding with them. They literally infiltrated into every ethnic organisation and made the most the leaderships of these organisations join the BJP," said a party insider who chose to remain anonymous.