NANDIGRAM, India — The challenger arrived with police vehicles, a band of drummers and the backing of the country’s powerful prime minister. The crowd joined him in full-throated chants of glory to the Hindu god Ram: “Jai Shree Ram!” He brought a warning: If Hindus did not unite around him, even their most basic religious practices would be in danger in the face of Muslim appeasement.
In another part of town, the incumbent took the stage in a wheelchair, the result of what she said was a politically motivated assault. Though her injuries kept her from stalking the stage in her white sari and sandals as usual, she still regaled the audience with taunts for the opposition. And she had a warning of her own: Her defeat would be a victory for an ideology that has no place for minorities like Muslims.
The monthlong election unfolding in the eastern Indian state of West Bengal is deeply personal. Mamata Banerjee, the state’s chief minister for the past decade, is facing off against her former protégé of 20 years, Suvendu Adhikari. He and dozens of other local leaders have defected from her party and are now allied with Narendra Modi, India’s prime minister.
But the heated vote could indicate something broader: whether anybody can stop Mr. Modi’s movement to reshape India’s secular republic into a Hindu-first nation.
Mr. Modi’s campaign is growing beyond its base in northern India, bringing him national and state victories. His Bharatiya Janata Party has reduced the main opposition group, the Indian National Congress, to a shadow of its past glory, pushing the country toward becoming a one-party democracy.
West Bengal represents a test of Mr. Modi’s Hindu nationalist reach. The state of 90 million people remains deeply proud of its Indigenous culture and tolerance of minorities. It is run by a strong regional leader with the heft and profile to challenge Mr. Modi directly.
Even if the B.J.P. loses when results are announced on May 2, a strong showing would help Mr. Modi signal that his party could be nearly unstoppable, said Vinay Sitapati, a professor of political science at Ashoka University who has chronicled the rise of the B.J.P.
“They would have shown that the B.J.P. is an all-India party, that our Hindu nationalism is capable of vernacular adaptation,” Mr. Sitapati said. “And that is a powerful symbol.”
Mr. Modi has put his brand front and center. He has traveled to West Bengal about a dozen times for packed rallies even as coronavirus cases rise. His face is all over the place, leading one B.J.P. worker to joke that he seems to be running for chief minister.
Mr. Modi and his lieutenants paint Ms. Banerjee as someone who has appeased Muslims, who make up about a quarter of the state’s population, at the expense of the Hindu majority. If she is re-elected, they say, she will turn West Bengal into another Bangladesh or Pakistan, where Hindu minorities are increasingly persecuted.
“If you don’t stamp on Lotus,” Mr. Adhikari said at a recent rally, referring to marking the logo of the B.J.P. on local ballots, “how will we be able to even celebrate the birth of Lord Ram here?”
Ms. Banerjee’s Trinamool Congress party has tried to frame the B.J.P. as outsiders who do not understand her state’s rich culture and have come to sow division. Her campaign slogan: “Bengal chooses its own daughter.”
Much of her campaign is built on her reputation as a tart-tongued political street fighter. Sympathizers with the local Communist Party once even beat her head with metal rods. She trounced the Communists in elections nevertheless.
Last month, in the midst of a jostling crowd, a car door slammed on Ms. Banerjee’s leg. She declared the incident a politically motivated attack, a contention her opponents have questioned. Still, her party has made her cast a symbol of a leader putting her body on the line for her cause.
“I am a pure cobra,” Mr. Chakraborty told one recent rally, as B.J.P. leaders behind him applauded. “One bite, and you will be at the cremation ground!”
Ms. Banerjee’s iron grip over state politics looms over the vote. The B.J.P. is trying to ride anti-incumbent sentiment fueled by her party’s corruption scandals and the way its members have used extortion and violence to keep power.
But Mr. Adhikari and many of the B.J.P.’s local candidates for the state’s 294-seat local assembly were themselves, until recently, members of her party. After decades of heavy-handedness by the Communists and Ms. Banerjee, Mr. Modi’s party began actively expanding in West Bengal only after he became prime minister in 2014, though its infrastructure is still lacking. One joke in the state holds that Trinamool will win a third term even if the B.J.P. prevails.
Ms. Banerjee’s success could depend on convincing voters that her party’s bad apples now work for the B.J.P. The B.J.P.’s dependence on Trinamool defectors has also led to a revolt among local Modi supporters who saw their presence as an insult to their years of work in the face of intimidation by the same people now chosen to represent them.
One defector, an 89-year-old assembly member named Rabindranath Bhattacharya, said he had switched parties only because Ms. Banerjee didn’t nominate him to serve a fifth term.
“I changed my party, but I am not changed,” Mr. Bhattacharya said in an interview at his house. Trinamool flags still hung from the trees and gate.
His candidacy moved hundreds of B.J.P. workers and supporters to pressure Mr. Bhattacharya to step aside. They went on a hunger strike, painted over party signs and ransacked the home of the local B.J.P. chief.
“We started here when no one dared speak as a B.J.P. member,” said Gautam Modak, who has worked for the B.J.P. in the district since 2003. “He got the party ticket three days after joining the B.J.P.”
Mr. Adhikari has said he defected from Ms. Banerjee’s camp because she and her nephew and heir-apparent, Abhishek Banerjee, use other party leaders as “employees” without sharing power. Still, in recent rallies he has put greater emphasis on identity politics, ending with chants of “Jai Shree Ram!”
Voting took place on Saturday in the town of Nandigram, a lush agricultural area, and both candidates were there. At rallies, crowds energized by their moment of power over sometimes abusive politicians braved the heat to listen, cheer and support. Turnout totaled 88 percent.
Satish Prasad Jana, a 54-year-old B.J.P. supporter at Mr. Adhikari’s rally, said he mainly supported Mr. Modi. He had no dispute with Ms. Banerjee except that she couldn’t control the abuse of her party workers, and he knew that some of those same people now work for Mr. Adhikari.
“I have 90 percent faith in Modi, 10 percent faith in Adhikari,” he said.
Hours later, a large rally of Ms. Banerjee’s supporters took place in a school courtyard surrounded by coconut trees. Women in colorful saris outnumbered men. They praised Ms. Banerjee’s government for paving the road that led to the school, for distributing rice at low prices and for making payments to families to keep their girls in school and prevent child marriage, among other initiatives.
But the energy was focused squarely on teaching Mr. Adhikari a lesson.
“You said Mamata is like your mother. The mother made you a leader, a minister, and in charge of the whole district,” said Suhajata Maity, a local leader, addressing Mr. Adhikari.
“Then, you stabbed the mother in her back.”
To resounding applause, she ended her speech with a call to the mothers in the crowd: “Will you teach him such a lesson that he abandons politics all together?”
Chandrasekhar Bhattacharjee contributed reporting.