Pete Buttigieg, the 37-year-old mayor of South Bend, Ind., announced on Wednesday that he was entering the Democratic presidential primary, embarking on a long-shot campaign that may test the appeal of a youthful, Midwestern profile over more traditional qualifications for the presidency.

In an email to potential supporters, Mr. Buttigieg (he pronounces it BOOT-edge-edge) said he was forming an exploratory committee and cast himself as a candidate of the future, stressing his generational identity and calling for policies “untethered to the politics of the past” on issues like climate and economic opportunity.

“What will America look like in 2054, when I reach the age of the current president?” Mr. Buttigieg said. “How will we look back on 2020?”