The breach in five districts — North 24-Parganas, South 24-Parganas, Calcutta, Howrah and Hooghly — which used to be the Trinamool Congress fortress, contributed the most to the BJP's landslide victory and thwarted Mamata Banerjee's dream of a fourth term.

These districts have 109 seats in all. Trinamool bagged more than 80 per cent of these seats in the 2011 and 2016 Assembly elections and over 85 per cent in the 2021 Assembly and 2024 Lok Sabha polls.

This time in 2026, Trinamool won 44 seats or only 40.37 per cent. The BJP won 63. The ISF won one (Bhangar) in South 24-Parganas. The Falta election has been countermanded, and a repoll is due on May 21.

“Trinamool's thumping win in the past two major elections was mainly based on the party's performance in this particular region. But as the BJP breached the area, Trinamool lost the election,” said a Calcutta-based political observer.

The picture was completely different in the 2021 Assembly polls when the Trinamool's statewide tally was 215. Trinamool had won 99 seats in this region, the BJP nine and the ISF one.

In the 2024 Lok Sabha polls when the TMC was ahead in 93 segments and the BJP led in only 16.

BJP sources said the results were unexpected even for them.

“We can't deny that we did not have the organisation here, contrary to north or western Bengal. Our lack of organisation was due to the terror unleashed by Trinamool in this region. But it was proved again that if people decide to oust somebody, no terror works,” a BJP leader claimed.

The BJP made major inroads in Calcutta, winning six of the 11 seats. The city backed Trinamool since its inception in 1998. In 2021, the Trinamool bagged all 11 seats, and in the 2024 Lok Sabha polls, it was ahead in nine segments.

In North 24-Parganas, the BJP won 24 of the 33 seats and Trinamool nine. In 2021, Trinamool had won 28 seats and the BJP five. In 2024, Trinamool led in 25 Assembly segments and the BJP in eight.

BJP insiders said they were astonished by the party's performance in South 24-Parganas, where it won 10 of 30 seats. “This was the fiefdom of Abhishek Banerjee, the Trinamool MP from Diamond Harbour. He unleashed terror in the district by using several criminal elements over the years in a way that common people could not vote for the past 10 years. Winning 10 seats is something the party will cherish,” a BJP insider claimed.

In Howrah, BJP won seven out of 16 seats. Trinamool had won all 16 seats in 2021 and taken leads in these Assembly segments in 2024.

The BJP showed a stellar score in Hooghly, winning 16 of its 18 seats. In 2021, Trinamool won 14 seats and in 2024 was ahead in 12 segments.