DES MOINES — Allison Kipp is all in for Senator Elizabeth Warren’s presidential campaign, but she was the exception.

Ben Miller, a 21-year-old student at Iowa State University, said he wants to vote for an economic populist, and if Senator Bernie Sanders runs again it will be a “tough choice” between him and Ms. Warren. Charles Miller, Ben’s father, said he expects to vote for Ms. Warren, but is also intrigued by a Democrat who could be described as her ideological opposite: Michael Bloomberg, the former mayor of New York.

“As Democrats, we haven’t seen a big field like this in a long time,” said the elder Mr. Miller, a 47-year-old resident of Ankeny, Iowa. “And as long as they keep it positive, as long as there’s no personal attacks and they just share their views, it’s going to be a good thing.”

“I’m ready to be convinced.”

Such is the mood of Iowa Democrats, who are currently feeling somewhat spoiled after a visit by Ms. Warren this weekend — more than a year before a single vote is cast in the state’s caucuses — unofficially kicked off the 2020 Democratic presidential primary. The party’s 2016 primary was defined by rigid and bitter lanes of Hillary Clinton and Mr. Sanders, but as the 2020 nomination process begins, the state’s voters are giddy at the prospect of a crowded field that could feature more than a dozen candidates across the ideological spectrum.