CEDAR RAPIDS, Iowa — Senators Kamala Harris and Elizabeth Warren took selfies — with each other. Senator Bernie Sanders marched with striking fast-food workers. Mayor Pete Buttigieg of South Bend, Ind., played the blues on an electric keyboard. And former Representative John Delaney brought a team of bagpipers.

The Democratic Party gathering in Iowa on Sunday, the state’s first major event of the 2020 election cycle, had the atmosphere of a circus, and one with a very, very big tent. The 19 presidential candidates in attendance chatted with reporters, gabbed with voters and tried to grab a breakout moment to distinguish themselves in the party’s historically crowded primary field.

A three-hour marathon of speeches by the candidates underscored the stratified reality of the early months of the primary race. There is a set of candidates — at most eight — who consistently break 2 percent in polling nationally and in early voting states, including Iowa.

Then, there is everyone else.

“They’re dividing it into the A group and the B group,” Senator Amy Klobuchar of Minnesota said. “I’m proud to be in the A group.”