Donald Trump, the 69-year-old New York real estate mogul and unrepentant bigot, is still dominating the Republican presidential primary polls. Trump’s sudden ascendance, accelerated by his willingness to insult virtually any ostensible ally within the conservative movement, has left GOP leaders dumbfounded. How did this caricature of a Republican politician, who has never held elected office, and whose personal ideology is remarkably fungible, usurp more experienced, more conservative, and better-funded candidates like Jeb Bush and Scott Walker?