CORNELIS, the 63-year-old governor of West Kalimantan, a province in Indonesian Borneo, is relaxing in jeans and a stained white vest at a table piled with krupuk crackers and other local snacks. Portraits of the governor and his wife posing with prize-winning vegetables (both are keen gardeners) decorate the walls of the family home in Ngabang, a town in the hills four hours’ drive from Pontianak, the provincial capital. But so do crucifixes and Christian figurines—and it is Mr Cornelis’s religion, more than anything else, that has made him the latest lightning rod for the Islamic Defenders Front (FPI), an Islamist vigilante group.

Around 90% of Indonesia’s 260m people are Muslim, but beyond the island of Java the population is much more mixed. Minorities watched with dismay as FPI and other Islamist groups turned on Basuki Tjahaja Purnama, the Christian and ethnic-Chinese governor of Jakarta, Indonesia’s capital, over cooked-up claims that he had insulted the Koran. Mr Basuki, known as Ahok, was defeated by a Muslim candidate in an election in April. Soon after a court sentenced him to prison for two years for blasphemy.

The government saw all this as an assault on Indonesia’s national motto—“Unity in diversity”—and on the five principles (known as pancasila) underpinning the constitution, which protects five officially recognised religions (Islam, Christianity, Hinduism, Buddhism and Confucianism). Joko Widodo, known as Jokowi, Indonesia’s mild-mannered president, has said that he will “crush” groups that imperil pancasila. On July 10th he signed a decree allowing the government to ban organisations with goals at odds with the constitution. On July 19th he duly banned Hizbut Tahrir, an outfit that campaigns for an Islamic caliphate. Rizieq Shihab, FPI’s leader, is lingering in Saudi Arabia after prosecutors charged him over sexually explicit messages that he is alleged to have exchanged with a woman on WhatsApp. (The law in question was passed at the insistence of religious parties in 2008.)

In West Kalimantan, however, the Islamists are on the march. They want to make sure that Mr Cornelis, who must step down next year having served the maximum two terms, is succeeded by a Muslim. Sixty percent of West Kalimantan’s 4.4m people are Muslim, but Mr Cornelis is one of 1.5m Christians, most of them from the Dayak ethnic group.

Mr Shihab has denounced Mr Cornelis as a kafir, or infidel. Mr Cornelis, asked what he thinks of FPI, stubs out a clove cigarette in an overflowing ashtray and says, “They are not welcome here. If they dare to come, we will butcher them.” Such talk is especially alarming in Kalimantan, where thousands were killed in fighting (pictured) between Dayaks and Muslim migrants from the island of Madura between 1996 and 2001. Attackers beheaded their enemies and even ate their organs in ghastly rituals. Back then, the Dayaks allied themselves with the Malays, a Muslim ethnic group, suggesting that the conflict was not about religion. But these days the dividing line seems to be primarily between Christians and Muslims.

Speaking at a traditional Dayak longhouse in the centre of Pontianak, not far from a shiny new “mega mall” that houses Starbucks, Wagamama and other Western chains, Kristianus Atok says that the campaign against Ahok shocked local people. “If we don’t stand together the Dayaks will be marginalised,” he concludes. As a member of a Dayak cultural organisation, Mr Atok travels regularly to remote corners of Borneo. Before the campaign against Ahok, relations between the communities had been good, he says. But lately there has been less mixing between them and people are frightened once again: “Everything is broken.”

It is not just Dayaks who are anxious. Subro, a Madurese member of Nahdlatul Ulama, a huge and moderate Muslim civic group, fled pogroms elsewhere in West Kalimantan in 1999. He now lives with his family on the edge of Pontianak, in an area where many displaced Madurese were resettled. Defaced posters of Mr Shihab line the bumpy road that leads to his home. “As Madurese, we are worried because there were bad days before,” he says.

In January an Islamist preacher from Jakarta, Tengku Zulkarnain, attempted to address a rally in Sintang, deep in West Kalimantan’s forests, but angry Dayak tribesmen brandishing swords chased him off. Local Muslim groups took offence. They organised a protest in Pontianak in May on the same day as an annual Dayak festival. Happily, the police managed to keep the rival groups apart.

Agus Setiadji is the 33-year-old leader of the United Malay People, one of the main groups behind the protest in Pontianak. He wears a traditional head-kerchief and a black T-shirt displaying two daggers above the slogan, “We are proud to be Malay”. Mr Setiadji complains that the Malays have been sidelined by Mr Cornelis. Government jobs and funds have gone only to the Dayaks, he says. Mr Setiadji predicts that if conflict comes, it will be worse than anything West Kalimantan has seen before: “We are ready for war.”