IOWA CITY, Iowa — Groundbreaking pollster George Gallup is known for founding the survey organization that tracks the nation’s opinion of the president, but he began his career with a more local concern: getting his mother-in-law elected to statewide office.

Ola Babcock Miller was a longshot in the 1932 race for Iowa Secretary of State. No woman had been elected to the office, and neither had a Democrat in 76 years. But Miller had a secret weapon.

Gallup, an advertising executive, conducted an informal poll of voters and learned that highway safety was a top concern, said his granddaughter, Alison Gallup. Miller ran on that issue, won a close race and founded what would become the Iowa State Patrol. The election changed Gallup’s life too: It got him hooked on political polling, the field that would make him a household name....