India’s prime minister, Narendra Modi, is a mesmerizing orator, in the way of a talk-show host with an acerbic tongue, and this month a campaign crowd of more than 50,000 showed up in Deoria, a hardscrabble town in the state of Uttar Pradesh, to hear his story. They knew and loved the part about how this son of a tea seller rose through the party ranks with no help from family connections. But the rest of his rags-to-power tale is changing fast.
Mr. Modi took office in 2014 billing himself as a pragmatic business reformer who could restart economic growth in