Indian Prime Minister Narendra Modi has come a long way. After being virtually banned from the U.S. for years over his failure to control anti-Muslim riots in his home state of Gujarat in 2002, he came to Washington for a triumphant first visit Monday with President Donald Trump—complete with bear hugs, defense deals and a welcoming tweet from the first lady.

The Hindu nationalist’s arrival in Washington was a reminder that of all the recent revolutions at the ballot box, Mr. Modi’s was the first. This week, pundits noted similarities between the two populist leaders: Both Mr. Trump and Mr. Modi have made political careers out of anti-Muslim animus, tapped nationalist passions, stoked the fires of intolerance and pursued vendettas against impertinent media outlets.

Yet these symmetries unfold in fundamentally different contexts. America has experienced a political upheaval, but it retains that supreme achievement of a mature democracy: It has two credible sides, left and right; the two sides have held, more or less; and the pendulum may swing again before long.

India has experienced something quite different in the three years since Mr. Modi took power. The “other side”—liberal India, secular India, the India of Nehru and Gandhi—hasn’t merely been decimated electorally; it has ceased to exist as a cultural and moral force. In area after area of life—from politics to media to cinema—there is now Mr. Modi’s India, and then a great void. The India of my childhood, with its fond notions of Hindu-Muslim unity, has gone under. It is as complete and comprehensive a defeat as one can imagine.

Last month, I traveled to Gorakhpur, in eastern Uttar Pradesh, India’s most populous state, where nearly 20% of the residents are Muslim. In state elections this March, Mr. Modi’s Bharatiya Janata Party, or BJP, won some 300 of the 400 seats. Mr. Modi’s choice of chief minister was Yogi Adityanath, a Hindu priest in saffron robes and longtime parliamentarian. His anti-Muslim rhetoric has been so hateful—he has told his followers that if Muslims “kill one Hindu man, then we will kill 100 Muslim men”—that he was once beyond the pale. Today, his popularity threatens to eclipse Mr. Modi’s. As S. Prasannarajan, the editor of Open magazine, told me recently, “Yogi Adityanath becoming chief minister of [Uttar Pradesh] is the single biggest event in Indian politics since Modi became chief minister of Gujarat.”