Most Iowa polls showed Donald Trump winning the state’s Republican caucuses. He didn’t. Some Iowa polls showed Hillary Clinton winning Iowa easily. She didn’t. It’s notoriously hard to poll Iowa, but what can pollsters learn from Monday night’s results to improve their work over the next few months — and for the 2020 caucuses?
One of the biggest lessons was a simple one: Keep on contacting voters as late as possible. CONT.
Carl Bialik, FiveThirtyEight