A spike in the price of onions has led to the ouster of governments in Indian elections in the past. Now, prices of the staple have collapsed, and many impoverished farmers are saying they will make Prime Minister Narendra Modi pay in next year's general election. Steep drops in recent weeks in the prices of onions and potatoes, both staple foods for India's 1.3 billion people, have badly hit the rural economy in large states. In interviews with dozens of farmers last week, Reuters reporters found resentment welling against Modi's Hindu nationalist Bharatiya Janata ...