ROUGH CUT (NO REPORTER NARRATION) Pete Buttigieg, the mayor of South Bend, Indiana, who has enjoyed a surge in opinion polls and a torrent of media coverage, formally launched a bid on Sunday for the 2020 Democratic presidential nomination.

The announcement in South Bend comes as little surprise.

No potential contender in the burgeoning Democratic field has seen as rapid a rise in the early stages of the campaign as Buttigieg, who went from obscure Midwestern politician to top-tier contender in a matter of weeks.

At 37, Buttigieg is the youngest entrant in a field that features 77-year-old U.S. Senator Bernie Sanders of Vermont and, likely soon, 76-year-old former Vice President Joe Biden - a contrast Buttigieg has emphasized in campaign events.

The man known as "Mayor Pete" has styled himself as the voice of the millennial generation, often talking about what the United States might look like decades from now.

He is the first openly gay major presidential candidate, which has given him inroads into a Democratic base that increasingly values diversity and progressivism.

As mayor of South Bend since 2012, he has presided over an economic turnaround that has brought new investment into the struggling northwestern Indiana industrial town, an achievement likely to be a central plank of his presidential campaign.