In 2002, rioters in the western Indian state of Gujarat savagely killed nearly 1,000 people, most of whom were part of the Muslim minority. Now, barely a decade later, Narendra Modi, who was the chief minister of Gujarat at the time and still holds the office, is a leading candidate to become prime minister of India.

Mr. Modi, a star of India’s main opposition party, the Bharatiya Janata Party, would become prime minister if the party won enough seats in parliamentary elections next summer with support from its political allies. His rise to power is deeply troubling to many Indians, especially the country’s 138 million Muslims and its many other minorities. They worry he would exacerbate sectarian tensions that have subsided somewhat in the last decade.

Supporters of Mr. Modi argue that an investigation commissioned by India’s Supreme Court cleared him of wrongdoing in the riots. And they insist that Mr. Modi, who is widely admired by middle-class Indians for making Gujarat one of India’s fastest-growing states, can revive the economy, which has been weakened by a decade of mismanagement by the coalition government headed by the Indian National Congress Party.

There is no question that the Congress Party has failed to capitalize on the economic growth of recent years to invest in infrastructure, education and public institutions like the judiciary. And instead of trying to revive itself with new ideas and leaders, it is likely to be led in the coming election by Rahul Gandhi, the inexperienced scion of the Nehru-Gandhi family.