A string of primary wins by progressive candidates has revealed the strength of a high-energy insurgent movement but also its possible limitations.

© Angelina Katsanis for The New York Times

Mr. Little, a former mayor and state senator, beat two other candidates. He focused on promises of banning corporate money from politics and supporting Medicare for all.

© Tim Gruber for The New York Times

In an upset, Luke Bronin, the former mayor of Hartford, won the Democratic nomination, capitalizing on calls for generational change.

© Jessica Hill/Associated Press

Senator Bernie Sanders warned that corporations have already lost control of technology that could cause “potentially cataclysmic results” for millions of people.

© Tierney L. Cross/The New York Times