“She’s got it all laid out,” said Susan Conroy, 71, a retired lawyer. “She’s got plans, and people are hungry for knowing, ‘Well, what are you going to do about it?’”

Several recent national polls have placed Ms. Warren at the front of the pack of candidates who are clustered behind Mr. Biden and Mr. Sanders. Ms. Warren has gained ground in polls over the past several weeks, while support for Mr. Sanders dipped after Mr. Biden joined the race.

At her events during a three-day visit to Iowa, Ms. Warren wove together the story of her upbringing in Oklahoma with a walk-through of her plans to achieve what she calls “big, structural change,” before taking a handful of questions.

“She was totally comfortable talking about any topic that anyone brought up, and you can tell she loves it,” said Frank Broz, 37, a small-business owner who went to see Ms. Warren in Fairfield. “I feel like any one of those topics, she could have spent another two hours on. That’s very persuasive to me.”