For much of his nearly year-old presidential campaign, Donald Trump bragged about his ability to best his Republican rivals without even hiring a pollster. But after quietly hiring his first high-profile data analyst, The New York Times reported last week that the real-estate magnate is considering bringing on more pollsters to help him with a bold goal: Winning the Democratic-heavy state of New York. While the Clinton campaign sees a map of 10 to 12 battleground states, including some Rust Belt states like Ohio and Pennsylvania, Trump's campaign claims he can be competitive in 15 states. That includes electorally rich,...