Pete Buttigieg, a little-known Indiana mayor who has risen to prominence in the early stages of the 2020 Democratic US presidential race, has made his official campaign entrance.

“I recognise the audacity of doing this as a Midwestern millennial mayor,” he said to cheers of “Pete, Pete, Pete” from an audience assembled in a former Studebaker car plant.

“More than a little bold, at age 37, to seek the highest office in the land.”

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In the hours after his announcement, more than one million dollars (£763,000) in donations poured in, said Lis Smith, speaking for the campaign.

The South Bend mayor, a Rhodes scholar and Afghanistan War veteran who has been essentially campaigning since January, has joined a dozen-plus rivals vying to take on President Donald Trump.

“The forces of change in our country today are tectonic,” he said.

“Forces that help to explain what made this current presidency even possible. That’s why, this time, it’s not just about winning an election – it’s about winning an era.”

Mr Buttigieg will return this week to Iowa and New Hampshire, which hold the nation’s first nominating contests, to campaign as a fully fledged candidate now being taken more seriously.

Over the past few months, Mr Buttigieg has appeared frequently on national TV news and talk shows and developed a strong social media following with his message that the country needs “a new generation of leadership”.

Mr Buttigieg’s poll numbers have climbed.

Pete Buttigieg announces that he will seek the Democratic presidential nomination during a rally in South Bend, IndianaPete Buttigieg announces that he will seek the Democratic presidential nomination during a rally in South Bend (Michael Conroy/AP)

Some polls put him behind only Vermont Senator Bernie Sanders, who sought the party’s nomination in 2016, and former vice president Joe Biden, who has not yet said he is running.

Mr Buttigieg’s campaign has raised more than seven million dollars (£5.3 million) in the first three months of this year, a total eclipsed by Mr Sanders’s leading 18 million dollars (£13.7 million) but more than senators Elizabeth Warren, Amy Klobuchar and Cory Booker.

“Right now, it’s pretty fun,” Mr Buttigieg said last month while visiting South Carolina , where he was met by larger-than-expected crowds.

His challenge is finding a way to sustain the momentum over the long term and avoiding becoming a “flavour of the month” candidate.

Scrutiny of his leadership in South Bend has increased, as has his criticism of vice president Mike Pence, who was Indiana’s governor when Mr Buttigieg was in his first term as mayor.

Mr Buttigieg would be the first openly gay nominee of a major presidential party; he married his husband Chasten last year.

Pete Buttigieg is joined by his husband Chasten Glezman before he announced that he will seek the Democratic presidential nomination during a rally in South Bend, IndianaPete Buttigieg is joined by his husband Chasten Glezman (Michael Conroy/AP)

He would be the first mayor to go directly to the White House.

And he would be the youngest person to become president, turning 39 the day before the next inauguration, on January 20 2021.

Theodore Roosevelt was 42 when he took office, while John F Kennedy was 43 and Bill Clinton 46.

The campaign kickoff speech echoed themes that have resonated with voters during Mr Buttigieg’s exploratory phase.

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He talks often about how political decisions shape people’s lives, including his own – from serving as a lieutenant in the navy reserve in 2014, to being able to marry his husband and to not having to worry about how to pay for his father’s hospital bills after his father’s death this year.

Mr Buttigieg also says the best way for Democrats to defeat Mr Trump may be to nominate a mayor experienced in helping to revive a Midwestern city once described as “dying”, rather than a politician who has spent years “marinating” in Washington.

Pete Buttigieg announces that he will seek the Democratic presidential nomination during a rally in South Bend, IndianaMr Buttigieg has raised millions in donations (Darron Cummings/AP)

He has criticised Mr Trump’s campaign slogan, Make America Great Again, saying the way to move the country forward is not to look backward or cling to an old way of life.

“There’s a myth being sold to industrial and rural communities: the myth that we can stop the clock and turn it back,” he said.

“It comes from people who think the only way to reach communities like ours is through resentment and nostalgia, selling an impossible promise of returning to a bygone era that was never as great as advertised to begin with.”

South Bend, which neighbours the University of Notre Dame, was hit hard by the decline of manufacturing, dating to the 1963 closing of the Studebaker car plant that cost thousands of residents their jobs.

The hulking, dilapidated factory loomed over the city for much of the past 60 years as what Mr Buttigieg called a daily reminder of South Bend’s past.

A volunteer vacuums water on the floor as they prepare for the announcement by Pete Buttigieg that he will seek the Democratic presidential nomination before a rally in South Bend, IndianaA volunteer vacuums water on the floor as they prepare for the announcement by Pete Buttigieg (Michael Conroy/AP)

Partially remodelled, it is now a mixed-use technology centre – and the setting for Mr Buttigieg’s announcement.

The South Bend fire marshal’s office said the rally drew more than 4,500 inside and 1,500 outside.

A steady stream of raindrops fell on speakers on the stage through the leaky roof.

“I like that he’s young,” said Tom Lacy, a 62-year-old retiree who came from Peoria, Illinois, for the event with his wife Candy on their 35th wedding anniversary.

“He’s so relatable. He doesn’t seem like a politician to me.

“The contrast between him and our current president is unbelievable.”

Nausher Ahmad Sial, a 68-year-old developer from South Bend, said “we need to try new blood”.

Mr Sial, who came to the US from Pakistan 35 years ago, said he has worked with Mr Buttigieg on development projects in the city and described the mayor as a “very honest, very fair guy”.